Light Emitting Device

ABSTRACT

By doping an organic compound functioning as an electron donor (hereinafter referred to as donor molecules) into an organic compound layer contacting a cathode, donor levels can be formed between respective LUMO (lowest unoccupied molecular orbital) levels between the cathode and the organic compound layer, and therefore electrons can be injected from the cathode, and transmission of the injected electrons can be performed with good efficiency. Further, there are no problems such as excessive energy loss, deterioration of the organic compound layer itself, and the like accompanying electron movement, and therefore an increase in the electron injecting characteristics and a decrease in the driver voltage can both be achieved without depending on the work function of the cathode material.

This application is a continuation of copending U.S. application Ser.No. 11/600,266, filed on Nov. 15, 2006 which is a continuation of U.S.application Ser. No. 10/304,238 filed on Nov. 26, 2002 (now U.S. Pat.No. 7,141,817 issued Nov. 28, 2006).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light emitting device and amanufacturing method thereof using a light emitting element which has afilm containing an organic compound (hereinafter referred to as an“organic compound layer”) between a pair of electrodes and which cangive fluorescence or luminescence by receiving an electric field. Thelight emitting device referred to in the present specification is animage display device, a light emitting device or a light source.Additionally, the following are included in examples of the lightemitting device: a module wherein a connector, for example, a flexibleprinted circuit (FPC) or a tape automated bonding (TAB) tape, or a tapecarrier package (TCP) is set up onto a light emitting element; a modulewherein a printed wiring board is set to the tip of a TAB tape or a TCP;and a module wherein integrated circuits (IC) are directly mounted on alight emitting element in a chip on glass (COG) manner.

2. Description of the Related Art

A light emitting element in the present invention is an element foremitting light by applying an electric field thereto. With respect tothe light emitting mechanism, it is said that an electron injected froma cathode and a hole injected from an anode are recombined in an organiccompound layer by applying a voltage to electrodes sandwiching anorganic compound layer to produce a molecule with an excitation state(hereinafter referred to as “a molecular exciton”) and the molecularexciton releases energy to emit light when it is returned to a groundstate.

In such a light emitting element, the organic compound layer isgenerally made from a thin film having a thickness less than 1 μm. Inaddition, since the light emitting element is a self-luminous typeelement such that the organic compound layer itself emits light, a backlight used in a conventional liquid crystal display is not required.Thus, it is the big advantage that an extremely thin and lightweightlight emitting element can be manufactured.

Also, when the carrier mobility of, for example, an organic compoundlayer having a thickness of about 100 nm to 200 nm is considered, aperiod from the injection of a carrier to the recombination is aboutseveral ten nanoseconds. Even when a period required for a process fromthe recombination of a carrier to light emission is included in theperiod, light emission is conducted within the order of microsecond.Thus, an extremely high response speed is one of characteristicsthereof.

From characteristics such as a thin type, lightweight, high speedresponsibility, and direct-current low-voltage drive, the light emittingelement has been noted as a next generation flat panel display element.In addition, since the light emitting element is a self-luminous typeand has a wide viewing angle, the visibility is relatively good. Thus,it is considered that the light emitting element is effective as anelement used for a display screen of a mobile electronic apparatus.

Tang et al. of Eastman Kodak company succeeded to obtain high luminanceand high efficiency that are sufficient to put into practicalapplication with luminance of 1000 cd/m² at 10 V or less and externalquantum efficiency of 1% by laminating organic compounds havingdifferent carrier transportation in order to improve the characteristicsof elements in which holes and electros are injected from each anodesand cathodes with sufficient balance and the thickness is set to 200 nmor less (Reference 1: Appl. Phys. Lett., 51, 913 (1987)). With respectto the high quantum efficiency elements, Tang uses Mg (magnesium) havingsmall work function to the organic compound that is basically regardedas insulators in order to lower the energy barrier generated withinjection of electrons from metal electrodes. However, Mg is easilyoxidizable, instable, and has poor adhesion property to the organicsurface, so that Mg is co-deposited with Ag (argentine) that isrelatively stable and has high adhesion property to the organic surfaceto be alloyed is used.

The group of Toppan Printing Company reported that lower driving voltageand higher luminescence than the element using Mg alloy by alloying Li(lithium) having smaller work function than Mg with Al (aluminum) inorder to stabilize as to use as cathode (Reference 2: 51st JapaneseSociety of Applied Physics Annual Meeting, Digest 28a-PB-4, p. 1040).

In light of the background art of the above-mentioned alloy electrodes,it has been desired to develop more stable cathodes. In recent years, ithas been reported that by interposing a cathode buffer layer made oflithium fluoride (LiF) or the like as a super-thin insulating layer (0.5nm), even an aluminum cathode can give luminescence property equivalentto or more than that of alloy of Mg and Ag, or the like alloy (Reference3: L. S. Hung, C. W. Tang and M. G. Mason: Applied Physics Letters, 70(2), 152 (1997).

The mechanism of the property improvement by disposing this cathodebuffer layer would be as follows: when LiF constituting the cathodebuffer layer is formed to contact Alq₃ constituting an electrontransport layer of an organic compound layer, the energy band of Alq₃ isbent to lower an electron injection barrier.

Another report is that improving the injection of electron from cathodeby reducing the electron injection barrier from cathode to the organiccompound layer by forming a metal doping layer in the organic compoundlayer contacting with a cathode of the light emitting element, thedoping layer is made from one or more metals from the following: alkalimetals having 4.2 eV or more work functions, alkaline earth metals, andtransition metals including rare earth metals (Japanese PatentApplication laid-open No. Hei 10-270171).

As described above, in a light emitting element composed of an anode, acathode and an organic compound layer, an invention is made forimproving the capability of injecting carriers from the electrode,resulting from an element characteristic of the light emitting element.

Further, there is another report that the carrier density according tothe improvement of hole injection and conductivity can be increased bydoping the electron acceptance materials to the hole transporting layercontacting with the anode of the light emitting element. Thus, a lowdriving voltage can be realized to (Reference 4: J. Blochwitz, M.Pfeiffer, T. Fritz, and K. Leo, Applied Physics Letters, vol. 73, No. 6,p. 729 (1998)).

However, with respect to the active matrix light emitting device, whenabove-described cathode buffer layer and metal doping layer are providedbetween the organic compound layer and the cathode in order to improvethe element characteristics of the light emitting element, the injectionfrom the cathode is improved, meanwhile, TFT characteristics isdeteriorated since the alkali metals and alkaline earth metals containedin a part of the cathode buffer layer and the metal doping layer arediffused to drift, and the TFT connected to the light emitting elementis influenced by that. Thus, the characteristics of the light emittingelement is improved, but then, the characteristics of TFT isdeteriorated.

By doping the electron acceptance material, the carrier densityaccording to the improvement of the hole injection and conductivity canbe increased, meanwhile, the organic compounds functioning as anacceptor is possible to form a charge-transfer complex. In the case thatthe charge-transfer complex exists at the interface with the lightemitting layer, an energy produced by recombination of carrier generatedon the light emitting layer moves to a non-luminous charge-transfercomplex to be quenched. The same is equally true of donor that improveselectron injection by doping the electron dose materials.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide the lightemitting element that has a mechanism to prevent the light emittingelement from quenching due to the removal of the energy produced byrecombination of carrier on the light emitting layer, and also improvethe carrier injection without using influential materials to TFTcharacteristics such as alkali metals and alkaline earth metals that areused conventionally.

In order to resolve the aforementioned problems, the present inventioncan form donor levels between the respective lowest unoccupied molecularorbitals (LUMOs) between a cathode and an organic compound layer. Thisis accomplished by doping an organic compound that functions as anelectron donor (hereinafter referred to as donor molecules) for applyingelectrons to the organic compound layer that contacts the cathode.Injection of electrons from the cathode and transmission of the injectedelectrons can therefore be performed with good efficiency. Further,there are no problems such as excessive energy loss accompanyingelectron movement and changes in quality of the organic compound layeritself, and therefore an increase in the electron injectingcharacteristics can be achieved, along with a lowering of drivervoltage, regardless of the work function of the cathode material.

In addition, there is no problem in that the donor molecules diffuse toreduce TFT characteristics, and therefore the characteristics of a lightemitting device can be improved without any of the pitfalls present whenalkaline metals or alkaline earth metals are used.

An electron transmitting region is formed in the present invention bydoping donor molecules into a portion of the electron transporting layercontained in the organic compound layer. Note that the electrontransmitting region formed here is formed to contact the cathode of thelight emitting device, and therefore the injecting characteristics ofelectrode from the cathode can be raised. In addition, there is anelectron transporting layer into which the donor molecules are notdoped, and therefore a structure in which there is no direct contactbetween the electron transmitting region and the light emitting layercan be formed.

For cases in which an electric charge transfer complex is formed by thedonor molecules in the electron transmitting region, if the electriccharge transfer complex exists in an interface with the light emittinglayer, this structure can prevent problems in which energy generated dueto carrier recombination in the light emitting layer is transferred tothe non-light emitting electric charge transfer complex, thus opticallyquenching light.

That is, the light emitting element of the present invention ischaracterized in that the organic compound layer is formed between ananode and the cathode. The organic compound layer has the light emittinglayer, and the electron transmitting region containing the donormolecules. The electron transmitting region is formed contacting theanode without contacting the light emitting layer.

According to a structure of the present invention, there is provided alight emitting device including: an anode; a cathode; and an organiccompound layer, the device being characterized in that: the organiccompound layer is formed between the anode and the cathode; the organiccompound layer has a light emitting layer and an electron transportinglayer; at least a portion of the electron transporting layer contactsthe cathode, through an electron transmitting region; and the electrontransmitting region contains donor molecules, and is formed to contactthe cathode.

Further, according to another structure of the present invention, thereis provided a light emitting device including: a TFT formed on aninsulating surface; an interlayer insulating film formed on the TFT; afirst electrode formed on the interlayer insulating film; an insulatinglayer formed covering an edge portion of the first electrode; an organiccompound layer formed on the first electrode; and a second electrodeformed on the organic compound layer, the device being characterized inthat: the TFT has a source region and a drain region; the firstelectrode is electrically connected to one of the source region and thedrain region; the organic compound layer has a light emitting layer andan electron transporting layer; at least a portion of the electrontransporting layer contacts the cathode through an electron transmittingregion; and the electron transmitting region is formed to contact thecathode.

In the light emitting device according to one of the above-mentionedstructures, when the first electrode is an anode and the secondelectrode is a cathode, the electron transmitting region is formed so asto be in contact with the second electrode, whereas when the firstelectrode is a cathode and the second electrode is an anode, theelectron transmitting region is formed so as to be in contact with thefirst electrode.

Further, from among a hole injecting layer, a hole transporting layer,the light emitting layer, a blocking layer, the electron transportinglayer, and the electron transmitting region formed in a portion of theelectron transporting region, the organic compound layer contains thelight emitting layer, the electron transporting layer, and the electrontransmitting region in each of the above-mentioned structures. Theelectron transmitting region is made from an organic compound containingdonor molecules.

In addition, a hole transmitting region containing acceptor moleculesmay also be formed in a portion of the hole transporting layer or thehole injecting layer in each of the above-mentioned structures. If thehole transmitting region is formed, then a structure is used in whichthe hole transmitting region is formed to contact the anode, andfurther, in which the hole transmitting region and the light emittinglayer do not have direct contact.

Note that although the light emitting device of the present inventionhas a structure suitable for an active matrix light emitting devicehaving light emitting elements electrically connected to TFTs, it isalso possible to implement the present invention in a passive lightemitting device.

Note that the luminescence obtained from the light emitting device ofthe present invention includes light emission from a singlet excitationstate, from a triplet excitation state, or from both types of excitationstates.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a diagram for explaining the element structure of a lightemitting device of the present invention;

FIGS. 2A and 2B are diagrams for explaining the element structure of anupward-emission type light emitting device;

FIG. 3 is a diagram for explaining the element structure of anupward-emission type light emitting device;

FIGS. 4A and 4B are diagrams for explaining the element structure of anupward-emission type light emitting device;

FIG. 5 is a diagram for explaining the element structure of anupward-emission type light emitting device;

FIGS. 6A and 6B are diagrams for explaining the element structure of adownward-emission type light emitting device;

FIG. 7 is a diagram for explaining the element structure of adownward-emission type light emitting device;

FIGS. 8A and 8B are diagrams for explaining the element structure of alight emitting device of the present invention;

FIGS. 9A and 9B are diagrams for explaining the element structure of alight emitting device of the present invention;

FIGS. 10A to 10C are diagrams for explaining a process of manufacturinga light emitting device of the present invention;

FIGS. 11A to 11C are diagrams for explaining the process ofmanufacturing the light emitting device of the present invention;

FIGS. 12A to 12C are diagrams for explaining the process ofmanufacturing the light emitting device of the present invention;

FIGS. 13A and 13B are diagrams for explaining the process ofmanufacturing the light emitting device of the present invention;

FIGS. 14A to 14D are diagrams for explaining the element structure ofthe light emitting device of the present invention;

FIGS. 15A and 15B are diagrams for explaining a circuit structurecapable of using the present invention;

FIGS. 16A and 16B are diagrams for explaining the element structure ofthe light emitting device of the present invention;

FIG. 17 is a diagram for explaining a passive matrix light emittingdevice;

FIGS. 18A to 18H are diagrams showing examples of electronic equipment;and

FIG. 19 is a diagram for explaining the element structure of the lightemitting device of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment Mode 1

The element structure of a light emitting device of the presentinvention is explained using FIG. 1.

An organic compound layer 103 is formed on an anode 102 in FIG. 1, and acathode 104 is formed on the organic compound layer 103. Note that holesare injected to the organic compound layer 103 from the anode 102, andelectrons are injected to the organic compound layer 103 form thecathode 104. The holes and the electrons recombine in the organiccompound layer 103, and thus luminescence is obtained.

Further, the organic compound layer 103 contains at least a holetransporting layer 111, a light emitting layer 112, an electrontransporting layer 113, and an electron transmitting region 114 formedin a portion of the electron transporting layer, and is formed from onelayer or a plurality of layers that are laminated, having differentfunctions with respect to carriers, such as a hole injecting layer, ahole transporting layer, or a blocking layer. Note that a case in whichthe organic compound layer 103 has a laminate structure composed of thehole transporting layer 111, the light emitting layer 112, the electrontransporting layer 113, and the electron transmitting region 114 isexplained in Embodiment Mode 1.

Light developed in an organic compound layer may be emitted from ananode side in the present invention, and may also be emitted from acathode side. Note that it is essential to form the anode by a materialthrough which light passes if light is emitted from the anode side, andthat the element characteristics can be increased greatly by forming thecathode by a material having light-shielding characteristics. Further,it is preferable to form the cathode by using a material through whichlight passes, and the anode by using a light-shielding material if lightis emitted from the cathode side.

A material having a large work function equal to or greater than 4.5 eVis used as a material for forming the anode 102 in order not to impedehole injection from the anode. Note that suitable materials differdepending on whether the anode has translucent characteristics orlight-shielding characteristics.

If the anode 102 is formed by a material through which light passes,then it can be formed by using a transparent conductive film such as anindium tin oxide (ITO) film, a transparent conductive film in which 2 to20% zinc oxide (ZnO) is mixed into indium oxide, IZO, or a materialcomposed of indium oxide and zinc oxide (In₂O₃—ZnO).

On the other hand, a metallic compound that is nitride or carbide of ametallic element residing in group 4, group 5, or group 6 of theperiodic table can be used for cases in which the anode 102 is formed bya light-shielding material. Preferably, the anode 102 can be formed byusing titanium nitride, zirconium nitride, titanium carbide, zirconiumcarbide, tantalum nitride, tantalum carbide, molybdenum nitride, ormolybdenum carbide.

Note that these metallic compounds have work functions equal to orgreater than 4.7 eV. For example, titanium nitride (TiN) has a workfunction of 4.7 eV. Further, the metallic compounds can be given anadditionally larger work function by ultraviolet radiation processingunder an ozone atmosphere (UV ozone processing).

The organic compound layer 103 is formed next. Note that known lowmolecular-based organic compounds, high molecular-based organiccompounds, and intermediate molecular-based organic compounds can beused as materials for forming the organic compound layer 103. Note thatthe term intermediate molecular-based organic compound denotesaggregates of organic compounds not having sublimation or meltingcharacteristics (with the number of molecules preferably equal to orless than 10), and organic compounds in which the molecular chain lengthis equal to or less than 5 μm (preferably equal to or less than 50 nm).

Note that organic compounds like those shown below can be used in theorganic compound layer 103 of the light emitting element formed inaccordance with Embodiment Mode 1.

The organic compound layer 103 is formed by laminating the holetransporting layer 111 made from a material having hole transportingcharacteristics, the light emitting layer 112 made from a materialhaving light emitting characteristics, the electron transporting layer113 made from a material having electron transporting characteristics,and the electron transmitting region 114 containing donor molecules in aportion of the electron transporting layer. Note that the laminatestructure of the organic compound layer in the present invention is notlimited to the structure shown here. In addition, it is also possible touse a laminate structure containing a hole injecting layer made from ahole injecting material, and a blocking layer (hole inhibiting layer)made from a material having hole blocking characteristics. Examples ofappropriate materials for each layer type are shown below. Note that thematerials used in the light emitting element of the present inventionare not limited to these.

As the hole transporting material used for forming the hole transportinglayer 111, an aromatic amine-based (that is, the one having a benzenering-nitrogen bond therein) compound is preferred. Widely used materialsinclude, for example, in addition to the above-mentioned TPD,derivatives thereof such as4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (hereafter, referred toas “α-NPD”). Also used are star burst aromatic amine compounds,including: 4,4′,4″-tris (N,N-biphenyl-amino)-triphenyl amine (hereafter,referred to as “TDATA”); and 4,4,4″-tris[N-(3-methylphenyl)-N-phenyl-amino]-triphenyl amine (hereafter, referredto as “MTDATA”).

Specific examples of the light emitting material used for forming thelight emitting layer 112 include metal complexes such as tris(8-quinolinolate) aluminum (hereafter, referred to as Alq₃), tris(4-methyl-8-quinolinolate) aluminium (hereafter, referred to as Almq₃),and bis(10-hydroxybenzo[h]-quinolinate) beryllium (hereafter, referredto as BeBq₂), and bis(2-methyl-8-quinolinolate)-(4-hydroxy-biphenylyl)-aluminum (hereafter,referred to as BAlq). The examples also include metal complexesincluding such as bis [2-(2-hydroxyphenyl)-benzooxazolate] zinc(hereafter, referred to as Zn(BOX)₂) andbis[2-(2-hydroxyphenyl)-benzothiazolate] zinc (hereafter, referred to asZn(BTZ)₂). Also, fluorescent dyes thereof may be used. Triplet lightemission materials may also be used and main examples thereof includecomplexes with platinum or iridium as central metal. Known triplet lightemission materials include tris (2-phenylpyridine) iridium (hereafter,referred to as Ir(ppy)₃), 2,3,7,8,12,13,17,18-octaethyl-21H, and23H-porphyrin-platinum (hereafter, referred to as PtOEP).

Metal complexes are often used as the electron transporting material.Preferred examples thereof include: metal complexes having a quinolineskeleton or benzoquinoline skeleton, such as the aforementioned Alq₃,Almq₃, BeBq₂; and mixed ligand complexes such as BAlq. Other examplesinclude metal complexes having oxazole-based and thiazole-based ligandssuch as Zn(BOX)₂ and Zn(BTZ)₂. Other materials that are capable oftransporting electrons than the metal complexes are: oxadiazolederivatives such as2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (hereafterreferred to as PBD), and1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazole-2-yl] benzene(hereafter, referred to as OXD-7); triazole derivatives such as3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenylyl)-1,2,4-triazole(hereafter, referred to as TAZ) and3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole(hereafter, referred to as p-EtTAZ); and phenanthroline derivatives suchas bathophenanthroline (hereafter, referred to as BPhen) andbathocuproin (hereafter, referred to as BCP).

Note that, in addition to the organic materials described above, it isalso is possible to use an inorganic material (specifically, materialssuch as Si and Ge oxides, carbon nitrides (CxNy), alkaline metalelements, alkaline earth metal elements, and materials in whichlanthanide element oxides are combined with Zn, Sn, V, Ru, Sm, or Ir) asa material used in a portion of the hole transporting layer 111, thelight emitting layer 112, or the electron transporting layer 113 of theorganic compound layer 103 of the present invention.

The electron transmitting region 114 is formed using donor moleculescontaining the molecular skeletons denoted by the following structuralformulae (D1) to (D7) in at least a portion therein, and an electrontransporting material. Note that, from the standpoint of increasing thetransporting characteristics of electrons injected, to the electroninjecting layer, and increasing the conductive characteristics of theelectron transmitting region, it is preferable that the structuralformulae (D1) to (D7) be contained at a level of 50% or more of theentire electron transmitting region 114.

In addition, if the organic compound layer contains a hole injectinglayer, then porphyrins are effective as hole injecting materials forforming the hole injecting layer, provided that the hole injectingmaterial used is an organic compound, and phthalocyanine (hereinafterreferred to as H₂—Pc), copper phthalocyanine (hereinafter referred to asCu—Pc), and the like may be used. There are also materials to whichchemical doping has been performed available as conductive highmolecular-based compounds, and polyethylene dioxythiophene (hereinafterreferred to as PEDOT) into which polystyrene sulfone (hereinafterreferred to as PSS) is doped, polyaniline, polyvinyl carbazole(hereinafter referred to as PVK), and the like can be given as examples.

In addition, for cases in which a blocking layer is included in theorganic compound layer, the above-mentioned BAlq, OXD-7, TAZ, p-EtTAZ,p-EtTAZ, BPhen, BCP, and the like are effective as hole blockingmaterials for forming the hole blocking layer because of their highexcitation energy level.

Note that a structure can be used in the present invention in which thematerials used in forming the hole transporting layer 111 and the lightemitting layer 112 are co-evaporated, forming a mixed layer in theinterface between the two layers. Similarly, it is also possible to usea structure in which a mixed layer is formed in the interface betweenthe light emitting layer 112 and the electron transporting layer 113.

The cathode 104 is formed next. A material having a small work functionequal to or less than 3.8 eV is used as the material forming the cathode104 in order to increase the injecting characteristics of electrons fromthe cathode 104. Note that it is preferable that the transmittivity of acathode 104 with respect to visible light be equal to or greater than40% for cases in which the cathode 104 has translucency. On the otherhand, the cathode 104 is formed by a film having a visible lighttransmittivity less than 10% for cases in which the cathode 104 haslight-shielding characteristics. For example, the cathode 104 may beformed by a single layer film of Al, Ti, W, or the like, or a laminatefilm with a material having a small work functions.

The light emitting element of the present invention, made from the anode102, the organic compound layer 103, and the cathode 104, and in whichthe electron transmitting region 114 is formed in a region where theorganic compound layer 103 contacts the cathode, can thus be formed.

Note that, although not shown in the figures, it is also possible toform a hole transmitting region in the present invention, not only theelectron transmitting region. The hole transmitting region is formed byusing acceptor molecules that contain the molecular skeletons denoted bythe following structural formulae (A1) to (A4) in at least a portiontherein, and a hole transporting material or a hole injecting material.Note that, from the standpoint of increasing the transportingcharacteristics of holes injected, and increasing the conductivecharacteristics of the hole transmitting region, it is preferable thatthe structural formulae (A1) to (A4) be contained at a level of 50% ormore of the entire hole transmitting region.

Embodiment Mode 2

The element structure of a light emitting element in a light emittingdevice formed in accordance with the present invention is explainedusing FIGS. 2A and 2B. Note that FIG. 2A is a diagram showing the crosssectional structure of a pixel portion of a light emitting devices andFIG. 2B is a diagram showing the element structure of a light emittingelement. Specifically, an upward-emission type element structure isexplained for a case in which one electrode is electrically connected toan electric current control TFT, and another electrode, formedsandwiching an organic compound layer therebetween, is a cathode madefrom a material through which light passes.

Thin film transistors (TFTs) are formed on a substrate 201 in FIG. 2A.Note that an electric control TFT which is electrically connected to afirst electrode to 210 of a light emitting element 215, and whichfunctions to control electric current supplied to the light emittingelement 215, and a switching TFT 221 for controlling a video signalapplied to a gate electrode of an electric current control TFT 222 areshown here.

A silicon substrate having light-shielding characteristics is used hereas the substrate 201, but a glass substrate, a quartz substrate, a resinsubstrate, and a flexible substrate material (plastic) may also be used.Further, active layers of each TFT are provided with at least a channelforming region 202, a source region 203, and a drain region 204.

Furthermore, the active layer of each TFT is covered by a gateinsulating film 205, and a gate electrode 206 is formed overlapping withthe channel forming region 202 through the gate insulating film 205. Aninterlayer insulating film 208 is formed covering the gate electrode206. Note that insulating films containing silicon, such as siliconoxide, silicon nitride, and silicon oxynitride films, and in addition,organic resin films of polyimide, polyamide, acrylic (includingphotosensitive acrylic) and BCB (benzocyclobutene) can be used asmaterials for forming the interlayer insulating film 208.

A wiring 207 which is electrically connected to the source region 203 ofthe electric current control TFT 222 is formed next on the interlayerinsulating film 208, and a first electrode 211 which is electricallyconnected to the drain region 204 is formed. Note that the firstelectrode 211 is formed so as to become an anode in Embodiment Mode 2.The first electrode (anode) 211 uses a material having a large workfunction and functioning as an anode. It is preferable that a conductivematerial having light-shielding characteristics and having highreflectivity be used as the material forming the first electrode 211.Further, it is preferable that the electric current control TFT 222 beformed by a p-channel TFT.

An insulating layer 212 is formed covering an edge portion of the firstelectrode (anode) 211, the wiring 207, and the like. A light emittingelement 215 can be completed by forming an organic compound layer 213 onthe first electrode (anode) 211, and forming a second electrode 214which becomes a cathode on the organic compound layer 213. Note that itis necessary to form the second electrode (cathode) 214 so that it haslight transmitting characteristics in Embodiment Mode 2, and thereforethe second electrode (cathode) 214 is formed to have a film thickness atwhich light (visible light) can pass.

The second electrode (cathode) 214 has light transmittingcharacteristics in Embodiment Mode 2, and therefore this becomes anupward-emission structure in which light developed due to recombinationof carriers in the organic compound layer 213 is emitted from the secondelectrode (cathode) 214 side.

The element structure of the light emitting element of the lightemitting device shown in FIG. 2A is explained next in detail using FIG.2B. In particular, the structure of elements formed using lowmolecular-based compounds in the organic compound layer is explained.

The first electrode (anode) 211 is formed by a light-shielding metalliccompound film. The first electrode (anode) 211 is an electrode which iselectrically connected with the electric current control TFT 222 shownin FIG. 2A, and is formed by sputtering using TiN at a film thickness of120 nm in Embodiment Mode 2. Note that bipolar sputtering, ion beamsputtering, opposing target sputtering, and the like may be used as thesputtering method here.

The organic compound layer 213 is then formed on the first electrode(anode) 211, and a hole injecting layer 231 functioning to increase theinjecting characteristics of holes from the anode is formed first. InEmbodiment Mode 2, a film formed from copper phthalocyanine (hereinafterreferred to as Cu—Pc) is formed by evaporation (resistance heatingmethod) at a film thickness of 30 nm as the hole injecting layer 231.

A hole transporting layer 232 is formed next by a material havingsuperior hole transporting characteristics. A film of4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (hereinafter referredto as α-NPD) is formed at a film thickness of 40 nm by evaporation here.

A light emitting layer 233 is formed next. Holes and electrons recombinein the light emitting layer 233 in Embodiment Mode 2, and luminescencedevelops. Note that the light emitting layer 233 is formed to have afilm thickness of 30 nm by co-evaporation using4,4′-dicarbazole-biphenyl (hereinafter referred to as CBP) as a hostmaterial having hole transporting characteristics, andtris(2-phenylpyridine) iridium (hereinafter referred to as Ir(ppy)₃), anorganic compound having light emitting characteristics.

In addition, a blocking layer 234 is formed. The blocking layer 235 isalso referred to as a hole inhibiting layer, and is a layer forpreventing useless electric current, that is not involved inrecombination, from flowing due to holes injected to the light emittinglayer 233 passing through the electron transporting layer and reachingthe cathode. Bathocuproin (hereinafter referred to as BCP) is formed ata film thickness of 10 nm by evaporation as the blocking layer 234 inEmbodiment Mode 2.

An electron transporting layer 235 is formed next. Note that theelectron transporting layer 235 is formed by an electron transportingmaterial that has electron accepting characteristics. Alq₃ is formed ata film thickness of 40 nm by evaporation as the electron transmittinglayer 235 in Embodiment Mode 2.

In addition, an electron transmitting region 236 can be formed byco-evaporating the electron transporting material with donor molecules.The organic compound layer 213 having a laminate structure is thuscompleted. Note that the electron transmitting region 236 is formedusing donor molecules containing the molecular skeletons shown by thestructural formulae (D1) to (D7) in at least a portion therein. A filmof the donor molecule 3,3′,5,5′-tetramethylbenzidine (hereinafterreferred to as TMB) and the electron transporting material Alq₃ isformed at a film thickness of 5 nm as the electron transmitting region236 by using co-evaporation in Embodiment Mode 2.

The second electrode 214 which becomes a cathode is formed next. Thesecond electrode (cathode) 214 is an electrode through which lightdeveloped in the organic compound layer 213 passes, and therefore isformed by a material through which light passes. Further, it isnecessary that the second electrode (cathode) 214 be formed by amaterial having a small work function because it is an electrode forinjecting electrons into the organic compound layer 213. Aluminum (Al)is formed at a film thickness of 20 nm in Embodiment mode 2, thusforming the second electrode (cathode) 214.

Note that the cathode is formed by an extremely thin film having athickness of approximately 10 to 30 nm in Embodiment Mode 2 in order toensure that its transmittivity is equal to or greater than 40%. However,it is not always necessary to make the film thickness thin, providedthat a material capable of sufficiently functioning as a cathode andcapable of ensuring a transmittivity equal to or greater than 40% isused.

In addition, the element structure for a case in which highmolecular-based compounds and low molecular-based compounds are used informing the organic compound layer in the light emitting device havingthe element structure of Embodiment Mode 2 is explained using FIG. 3.

A first electrode (anode) 301 is formed by a metallic compound filmhaving light-shielding characteristics, similar to FIG. 2B. However, anorganic compound layer 302 formed on the first electrode (anode) 301differs from that of FIG. 2B. The organic compound layer 302 has alaminate structure made form a hole transporting layer 303, a lightemitting layer 304, an electron transporting layer 305, and an electrontransmitting region 306 formed in a portion of the electron transportinglayer 305. Note that a case in which the hole transporting layer 303 andthe light emitting layer 304 are formed using high molecular-basedcompounds is explained.

The hole transporting layer 303 can be formed by using both of PEDOT(poly(3,4-ethylene dioxythiophene)) and polystyrene sulfone (hereinafterreferred to as PSS). In addition, the hole transporting layer 303 canalso be formed by using both of polyaniline (hereinafter referred to asPANI) and camphor sulfonic acid (hereinafter referred to as CSA). Notethat these materials are water soluble, and therefore film formation isperformed by application of an application liquid, manufactured bydissolving the materials in water, using spin coating. Note also thatthe hole transporting layer 303 is formed by a film made from PEDOT andPSS at a film thickness of 30 nm in Embodiment Mode 2.

Also, for the light emitting layer 304, polyparaphenylenevinylene-based, polyparaphenylene-based, polythiophene-based orpolyfluorene-based material may be used.

As the polyparaphenylene vinylene-based material, materials such aspolyparaphenylene vinylene (poly(p-phenylene vinylene)) (hereafterreferred to as PPV), or poly[2-(2′-ethyl-hexoxy)-5-methoxy-1,4-phenylenevinylene](hereafter referred to as MEH-PPV), which can emit an orangelight, and materials such as poly [2-(dialkoxyphenyl)-1,4-phenylenevinylene] (hereafter referred to as ROPh-PPV) which can emit a greenlight.

As the polyparaphenylene-based material, materials such aspoly(2,5-dialkoxy-1,4-phenylene) (hereafter referred to as RO—PPP),poly(2,5-dihexoxy-1,4-phenylene), and the like which can emit a bluelight.

As the polythiophene-based material, materials such aspoly[3-alkylthiophene](hereafter referred to as PAT),poly[3-hexylthiophene] (hereafter referred to as PHT),poly[3-cyclohexylthiophene] (hereafter referred to as PCHT),poly[3-cyclohexyl-4-methylthiophene](hereafter referred to as PCHMT),poly[3,4-dicyclohexylthiophene] (hereafter referred to as PDCHT),poly[3-(4-octylphenyl)-thiophene] (hereafter referred to as POPT),poly[3-(4-octylphenyl)-2,2-bithiophene] (hereafter referred to as PTOPT)which can emit a red light.

Further, as the polyfluorene-based material, materials such aspoly(9,9-dialkylfluorene)(hereafter referred to as PDAF), orpoly(9,9-dioctylfluorene)(hereafter referred to as PDOF) which can emita blue light.

Note that, these materials are obtained by applying solution obtained bydissolving the materials in an organic solvent using the applicationmethod. Examples of the organic solvent used here include toluene,benzene, chlorobenzene, dichlorobenzene, chloroform, tetralin, xylene,dichloromethane, cyclohexane, NMP (N-methyl-2-pyrrolidone), dimethylsulfoxide, cyclohexanone, dioxane and THF (tetrahydrofuran).

Note that the light emitting layer 304 is formed in Embodiment Mode 2 tohave a film thickness of 80 nm by spin coating or ink jet printing usingan application liquid manufactured by dissolving PPV in toluene.

An electron transporting layer 305 is formed next on the light emittinglayer 304. Note that the low molecular-based compound Alq₃ is used asthe material for forming the electron transporting layer 305, and isformed at a film thickness of 40 nm.

In addition, the organic compound layer 302 is completed to have alaminate structure by forming an electron transmitting region 306 byco-evaporating the material having electron transportingcharacteristics, which is used for forming the electron transportinglayer 305, with donor molecules. Note that TMB and Alq₃ are formed hereat a film thickness of 5 nm by co-evaporation as the electrontransmitting region 306, similar to FIG. 2B.

A second electrode (cathode) 307 is formed lastly, thus completing thelight emitting element. Note that the second electrode (cathode) 307formed here is formed by laminating 20 nm of Al, similar to the caseexplained in FIG. 2B.

Embodiment Mode 3

A light emitting device in which the element structure of a lightemitting element differs from that of the light emitting devicedescribed in Embodiment Mode 2 is explained in Embodiment Mode 3 usingFIGS. 4A and 413. FIG. 4A is a diagram showing the cross sectionalstructure of a pixel portion of the light emitting device, and FIG. 4Bis a diagram showing the element structure of the light emittingelement. Specifically, an upward-emission type element structure isexplained for a case in which one electrode is electrically connected toan electric current control TFT, and another electrode, formedsandwiching an organic compound layer therebetween, is an anode madefrom a material through which light passes.

Note that the light emitting device in Embodiment Mode 3 has an electriccurrent control TFT 422 and a switching TFT 421 on a substrate 401,similar to that of Embodiment Mode 2, and it is preferable that theelectric current control TFT 422 be formed by an n-channel TFT inEmbodiment Mode 3.

An interlayer insulating film 408 is formed covering the electriccurrent control TFT 422 and the switching TFT 421. A wiring 407 that iselectrically connected to a source region 403 of the electric currentcontrol TFT 422, and a first electrode 411 that is electricallyconnected to a drain region 404 of the electric current control TFT 422are then formed on the interlayer insulating film 408. Note that thefirst electrode 411 is formed so as to become a cathode in EmbodimentMode 3. An insulating layer 412 is formed covering an edge portion ofthe first electrode 411, the wiring 407, and the like. The firstelectrode (cathode) 411 thus uses a material having a small workfunction that functions as a cathode. Note that it is preferable to usea conductive material having light-shielding characteristics and havinghigh reflectivity as the material for forming the first electrode(cathode) 411. Reference numerals 402 denotes a channel formationregion, 405 denotes a gate insulating film, and 406 denotes a gateelectrode.

Further, an organic compound layer 413 is formed on the first electrode(anode) 411, and a second electrode 414 which becomes an anode is formedon the organic compound layer 413, thus completing a light emittingelement 415. Note that it is necessary that the second electrode (anode)414 be formed having light transmitting characteristics in EmbodimentMode 3, and therefore the second electrode (anode) 414 is formed by atransparent conductive film through which light (visible light) passes.

The element structure becomes an upper surface emission structure inEmbodiment Mode 3 in which light developed due to carrier recombinationin the organic compound layer 413 is emitted from the second electrode(anode) 414 side because a transparent conductive film is used as thesecond electrode (anode) 414. Note that it is preferable to form thefirst electrode (cathode) 411 by a material having light-shieldingcharacteristics in Embodiment Mode 3.

The element structure of the light emitting element of the lightemitting device of FIG. 4A is explained next in detail using FIG. 4B. Inparticular, the structure of an element formed by using lowmolecular-based compounds in the organic compound layer is explained.

The first electrode (cathode) 411 is formed by a conductive film havinglight-shielding characteristics. The first electrode (cathode) 411 is anelectrode that is electrically connected to the electric current controlTFT 422 in Embodiment Mode 3 as shown in FIG. 4A, and is formed by Alformed at a film thickness of 110 nm. Note that evaporation is used infilm formation.

The organic compound layer 413 is then formed on the first electrode(cathode) 411, and an electron transmitting region 431 is formed first.Note that the electron transmitting region 431 is formed byco-evaporating donor molecules containing the molecular skeletons shownby the structural formulae (D1) to (D7) in at least a portion therein,and a material having electron transporting characteristics and used forforming an electron transporting layer 432, which is formed next. Theelectron transmitting region 431 is formed in Embodiment Mode 3 byco-evaporating TMB and Alq₃ at a film thickness of 5 nm.

The electron transporting layer 432 which functions to increase theelectron transporting characteristics is formed next. The electrontransporting layer 432 is formed by an electron transporting materialhaving electron accepting characteristics. A film of Alq₃ is formed at afilm thickness of 40 nm as the electron transporting layer 432 inEmbodiment Mode 3 by evaporation.

A blocking layer 433 is formed next. The blocking layer 433, alsoreferred to as a hole inhibiting layer, is a layer for preventinguseless electric current, that is not involved in recombination, fromflowing due to holes injected to a light emitting layer 434 passingthrough the electron transporting layer 432 and reaching the firstelectrode (cathode) 411. BCP is formed at a film thickness of 10 nm byevaporation as the blocking layer 433 in Embodiment Mode 3.

The light emitting layer 434 is formed next. Holes and electronsrecombine in the light emitting layer 434 in Embodiment Mode 3, andluminescence develops. Note that the light emitting layer 434 is formedat a film thickness of 30 nm by co-evaporation using CBP as a hostmaterial having hole transporting characteristics, and the lightemitting organic compound Ir(ppy)₃.

A hole transporting layer 435 is formed next from a material havingsuperior hole transporting characteristics. A 40 nm thick film of α-NPDis formed here by evaporation.

A hole injecting layer 436 is formed lastly, thus completing the organiccompound layer 413 having a laminate structure. Note that the holeinjecting layer 436 functions to increase the injecting characteristicsof holes from the anode. Cu—Pc is formed at a film thickness of 30 nm asthe hole injecting layer 436 in Embodiment Mode 3. Note that evaporationis used in the formation.

The second electrode 414 which becomes an anode is formed next. In thepresent invention, the second electrode (anode) 414 is an electrodethrough which light developed in the organic compound layer 413 passes,and therefore is formed by a material having light transmittingcharacteristics. Further, the second electrode (anode) 414 is anelectrode that injects holes into the organic compound layer 413, andtherefore it is necessary to form the second electrode (anode) 414 by amaterial having a high work function. Note that, in this embodimentmode, an ITO film or a transparent conductive film in which 2 to 20%zinc oxide (ZnO) is mixed into indium oxide is used as the material forforming the second electrode (anode) 414, and is formed by sputtering toa film thickness of 100 nm. Note that other known materials (such as IZOor materials made form indium oxide and zinc oxide) can also be used forforming the second electrode (cathode) 414, provided that they aretransparent conductive films having a large work function.

In addition, the element structure for a case of forming the organiccompound layer by using high molecular-based compounds and lowmolecular-based compounds in the light emitting device having theelement structure of Embodiment Mode 3 is explained using FIG. 5.

A first electrode (cathode) 501 is formed by a conductive film havinglight-shielding characteristics, similar to that of FIG. 4B. However, anorganic compound layer 502 formed on the first electrode (cathode) 501differs from that of FIG. 4B. The organic compound layer 502 is madeform a laminate structure of an electron transmitting region 503, anelectron transporting layer 504, a light emitting layer 505, and a holetransporting layer 506. Note that a case in which high molecular-basedcompounds are used in the light emitting layer 505 and the holetransporting layer 506 is explained here.

The electron transmitting region 503 is formed on the first electrode(cathode) 501. Here, as the electron transmitting region 503, TMB andAlq₃ are deposited with a film thickness of 5 nm by co-evaporation,similar to that explained in FIG. 4B.

The electron transporting layer 504 is formed next on the electrontransmitting region 503. Note that, as the low molecular-based compound,Alq₃ is used as a material for forming the electron transporting layer504 here, and is formed by evaporation to a film thickness of 40 nm.

An application liquid obtained by dissolving PPV in toluene is appliednext by spin coating, forming an 80 nm-thick film as the light emittinglayer 505.

The hole transporting layer 506 is formed next, thus completing theorganic compound layer 502 having a laminate structure. Note that thehole transporting layer 506 is formed in Embodiment Mode 3 by applyingan application liquid, obtained by dissolving PEDOT and PSS in water,using spin coating. The hole transporting layer 506 is formed at a filmthickness of 30 nm in Embodiment Mode 3.

A second electrode (anode) 507 is formed lastly, thus completing thelight emitting element. Note that the second electrode (anode) 507formed here is formed by forming through sputtering an indium tin oxide(ITO) film or a transparent conductive film in which 2 to 20% zinc oxide(ZnO) is mixed into indium oxide, similar to that shown in FIG. 4B.

Embodiment Mode 4

A light emitting device in which the element structure of a lightemitting element differs from that disclosed by Embodiment Mode 2 orEmbodiment Mode 3 is explained in Embodiment Mode 4 using FIGS. 6A and6B. Note that FIG. 6A is a diagram showing the cross sectional structureof a pixel portion of the light emitting device, and FIG. 6B is adiagram showing the element structure of the light emitting element.Specifically, a downward-emission element structure for a case in whichan electrode that is electrically connected to an electric currentcontrol TFT is an anode made from a material having light transmittingcharacteristics is explained.

Note that an electric current control TFT 622 and a switching TFT 621are formed on a substrate 601 in the light emitting device of EmbodimentMode 4, similar to Embodiment Mode 2 and Embodiment Mode 3. However, itis preferable that the electric current control TFT 622 be formed by ap-channel TFT in Embodiment Mode 4.

A wiring 607 which is electrically connected to a source region 603 ofthe is electric current control TFT 622, and a first electrode 611 whichis electrically connected to a drain region 604 of the electric currentcontrol TFT 622 are formed on an interlayer insulating film 608 formedcovering the electric current control TFT 622 and the switching TFT 621.Note that the first electrode 611 is formed so as to become an anode inEmbodiment Mode 4. The first electrode (anode) 611 is formed using amaterial having a large work function and functioning as an anode. Aninsulating layer 612 is formed covering an edge portion of the firstelectrode (anode) 611, the wiring 607, and the like. Note that it ispreferable to use a conductive material having light transmittingcharacteristics as the material for forming the first electrode (anode)611. Reference numeral 602 denotes a channel formation region, 605denotes a gate insulating film, and 606 denotes a gate electrode.

Further, a glass substrate is used as a substrate having lighttransmitting characteristics for the substrate 601, but a quartzsubstrate may also be used.

Furthermore, an organic compound layer 613 is formed on the firstelectrode (anode) 611, and a light emitting element 615 can be completedby forming a second electrode 614 which becomes a cathode on the organiccompound layer 613. Note that it is necessary that the first electrode(anode) 611 be formed so as to have light transmitting characteristicsin Embodiment Mode 4, and therefore the first electrode (anode) 611 isformed by a transparent conductive film through which light (visiblelight) passes. Note also that it is preferable to form the secondelectrode (cathode) 614 by a material having light-shieldingcharacteristics.

A transparent conductive film is used in the first electrode (anode) 611in Embodiment Mode 4, and therefore this is a lower surface emissionstructure in which light developed by carrier recombination in theorganic compound layer 613 is emitted from the first electrode (anode)611 side.

The element structure in the light emitting element of the lightemitting device explained in FIG. 6A is explained next in detail usingFIG. 6B. In particular, an element structure obtained by using lowmolecular-based compounds in the organic compound layer is explained.

The first electrode (anode) 611 is formed by a transparent conductivefilm having light transmitting characteristics. The first electrode(anode) 611 is an electrode that is electrically connected to theelectric current control TFT 622 in Embodiment Mode 4, as shown in FIG.6A, and an indium tin oxide (ITO) film or a transparent conductive filmin which 2 to 20% zinc oxide (ZnO) is mixed into indium oxide is used asthe material forming the first electrode (anode) 611 in Embodiment Mode4. The film is formed with a film thickness of 100 nm by sputtering.

The organic compound layer 613 is then formed on the first electrode(anode) 611, and a hole injecting layer 631 functioning to increase theinjecting characteristics of holes from the anode is formed first. InEmbodiment Mode 4, Cu—Pc is deposited by evaporation at a film thicknessof 30 nm as the hole injecting layer 631.

A hole transporting layer 632 is formed next by a material havingsuperior hole transporting characteristics. A 40 nm-thick film of α-NPDis formed here by sputtering.

A light emitting layer 633 is formed next. Holes and electrons recombinein the light emitting layer 633 in Embodiment Mode 4, and light emissionoccurs. Note that the light emitting layer 633 is formed at a filmthickness of 30 nm by co-evaporation using CBP as a host material havinghole transporting characteristics and Ir(ppy)₃ as the light emittingorganic compound.

In addition, a blocking layer 634 is formed. The blocking layer 634 isalso referred to as a hole inhibiting layer, and is a layer forpreventing useless electric current, that is not involved inrecombination, from flowing when holes injected to the light emittinglayer 633 pass through an electron transporting layer to reach acathode. BCP is deposited at a film thickness of 10 nm by evaporation asthe blocking layer 634 in Embodiment Mode 4.

An electron transporting layer 635 is then formed. Note that theelectron transporting layer 635 is formed by an electron transportingmaterial having electron accepting characteristics. A 40 nm-thick filmof Alq₃ is formed by evaporation in Embodiment Mode 4 as the electrontransporting layer 635.

In addition, an electron transmitting region 636 can be formed byco-evaporation of a material having electron transportingcharacteristics and donor molecules, and the organic compound layer 613having a laminate structure is thus completed. Note that the electrontransmitting region 636 is formed by co-evaporation of donor moleculescontaining the molecular skeletons shown by structural formulae (D1) to(D7) in at least a portion therein, and a material having electrontransporting characteristics. As the electron transmitting region 636,TMB and Alq₃ are deposited in Embodiment Mode 4 having a film thicknessof 5 nm by co-evaporation.

The second electrode 614 which becomes a cathode is formed next. Thesecond electrode (cathode) 614 is an electrode for injecting electronsinto the organic compound layer 613 in the present invention, andtherefore it is necessary that it be formed by using a material having asmall work function. The second electrode (cathode) 614 is formed fromAl with a film thickness of 110 nm in Embodiment Mode 4. Note thatevaporation is used here in the film formation.

In addition, the element structure for a case of using highmolecular-based compounds and low molecular-based compounds in theorganic compound layer in the light emitting device having the elementstructure of Embodiment Mode 4 is explained using FIG. 7.

A first electrode (anode) 701 is formed from a transparent conductivefilm having light transmitting characteristics, similar to FIG. 6B.However, an organic compound layer 702 formed on the first electrode(anode) 701 is made from a laminate structure of a hole transportinglayer 703, a light emitting layer 704, an electron transporting layer705, and an electron transmitting region 706. Note that a case of usinghigh molecular-based compounds in the hole transporting layer 703 andthe light emitting layer 704 is explained here.

The electron transporting layer 703 is formed on the first electrode(anode) 701. A film formed by application using spin coating of anapplication liquid, obtained by dissolving PEDOT and PSS in water, isused here as the hole transporting layer 703. Note that the holetransporting layer 703 is formed at a film thickness of 30 nm inEmbodiment Mode 4.

The light emitting layer 704 is formed next on the hole transportinglayer 703. Note that a film formed by application using spin coating ofan application liquid, obtained by dissolving PAT in toluene, is usedhere with a film thickness of 80 nm as the light emitting layer 704.

The electron transporting layer 705 is formed next on the light emittinglayer 704. Note that a film formed by evaporation using Alq₃ as the lowmolecular-based compound that is a material for forming the electrontransporting layer 705 is used here with a film thickness of 40 μm asthe electron transporting layer 705.

The electron transmitting region 706 is formed next. The electrontransmitting region 706 is formed here at a film thickness of 5 nm byco-evaporating TMB and Alq₃, similar to that explained in FIG. 6B.

A second electrode (cathode) 707 is formed lastly, completing the lightemitting element. Note that the second electrode (cathode) 707 formedhere is formed by Al at a film thickness of 110 nm, similar to thatshown in FIG. 6B.

Embodiment Mode 5

An element structure of a light emitting element having a holetransmitting region 805 in a region where a first electrode 802 thatbecomes an anode is brought into contact with an organic compound layer803, and having an electron transmitting region 809 in a region where asecond electrode 804 that becomes a cathode is brought into contact withthe organic compound layer 803, as shown in FIG. 8A, is explained nextin Embodiment Mode 5. Reference numeral 806 denotes a hole transportinglayer, 807 denotes a light emitting layer, and 808 denotes an electrontransporting layer.

FIG. 8B shows a structure in which the upward-emission light emittingelement explained in Embodiment Mode 2 additionally has a holetransmitting region 821 in a region at which the first electrode 802,which is the anode, and the organic compound layer 803 contact.

That is, the hole transmitting region 821 is formed on the firstelectrode (anode) 802 at a film thickness of 30 nm by co-evaporatingTCNQ, which is an acceptor molecule, and α-NPD, which is a materialhaving hole transporting characteristics.

A hole transporting layer 822 is then formed on the hole transmittingregion 821 by forming a 40 nm-thick film of α-NPD using evaporation.

Note that a light emitting layer 823, a blocking layer 824, an electrontransporting layer 825, and an electron transmitting region 826 areformed on the hole transporting layer 822, similar to the structureshown in FIG. 2B, thus forming the organic compound layer 803 having alaminate structure.

The second electrode (cathode) 804 is formed lastly by depositing Al ata film thickness of 20 nm, thus forming the upward-emission lightemitting device having the hole transmitting region 821 and the electrontransmitting region 826.

The element structure of a light emitting element, in which the lightemitting element structure explained in Embodiment Mode 3 has further ahole transmitting region 916 in a region at which a second electrode904, which is an anode, and an organic compound layer 903 contact, asshown in FIG. 9A, is explained next.

Note that an electron transmitting region 911, an electron transportinglayer 912, a blocking layer 913, a light emitting layer 914, and a holetransporting layer 915 are formed on a first electrode 902, which isobtained by forming a 110 nm-thick film of Al, similar to the structureshown in FIG. 4B.

The hole transmitting region 916 is formed at a film thickness of 30 nmon the hole transporting layer 915 by co-evaporation using TCNQ as anacceptor molecule, and α-NPD as a hole transporting material.

The second electrode (anode) 904 is formed lastly by depositing ITO witha film thickness of 120 nm, thus forming the upward-emission lightemitting device having the electron transmitting region 911 and the holetransmitting region 916.

The element structure of a light emitting element, in which thedownward-emission light emitting element structure explained inEmbodiment Mode 4 has further a hole transmitting region 931 in a regionat which a first electrode 922, which is an anode, and an organiccompound layer 923 contact, as shown in FIG. 9B, is explained next.

That is, the hole transmitting region 931 is formed at a film thicknessof 30 nm on the first electrode (anode) 922, obtained by forming 120nm-thick film of ITO, by co-evaporation using TCNQ as an acceptormolecule, and α-NPD as a material having hole transportingcharacteristics.

A hole transporting layer 932 is formed on the hole transmitting region931 by evaporating α-NPD to a film thickness of 40 nm.

Note that a light emitting layer 933, a blocking layer 934, an electrontransporting layer 935, and an electron transmitting region 936 areformed on the hole transporting layer 932, similar to the structureshown in FIG. 6B, thus forming the organic compound layer 923 having alaminate structure.

A second electrode (cathode) 924 is formed lastly by forming a 110nm-thick film of Al, thus completing the upward-emission light emittingdevice having the hole transmitting region 931 and the electrontransmitting region 936.

Embodiment Mode 6

This embodiment mode will be described with references to FIGS. 10A to133B. Here, a detailed description will be given on a method ofmanufacturing a pixel portion and TFTs (n-channel TFTs and p-channelTFTs) of a driving circuit that are provided in the periphery of thepixel portion are formed on the same substrate at the same time. In thisembodiment mode, the light emitting element having the element structureshown in Embodiment Mode 2 is formed.

The base insulating film 601 is formed on the substrate 600 to obtainthe first semiconductor film having a crystal structure. Subsequently,isolated in island-shape semiconductor layers 602 to 605 are formed byconducting etching treatment to the desired shape.

As a substrate 600, the glass substrate (#1737) is used. As a baseinsulating film 601, a silicon oxynitride film 601 a is formed as alower layer of a base insulating film on the silicon oxide film byplasma CVD at a temperature of 400° C. using SiH₄, NH₃, and N₂O asmaterial gas (the composition ratio of the silicon oxynitride film:Si=32%, O=27%, N=24%, H=17%). The silicon oxynitride film has athickness of 50 nm (preferably 10 to 200 nm). The surface of the film iswashed with ozone water and then an oxide film on the surface is removedby diluted fluoric acid (diluted down to 1/100). Next, a siliconoxynitride film 601 b is formed as an upper layer of the base insulatingfilm by plasma CVD at a temperature of 400° C. using SiH₄ and N₂O asmaterial gas (the composition ratio of the silicon oxynitride film:Si=32%, O=59%, N=7%, H=2%). The silicon oxynitride film 601 b has athickness of 100 nm (preferably 50 to 200 nm) and is laid on the lowerlayer to form a laminate. Without exposing the laminate to the air, asemiconductor film having an amorphous structure (here, an amorphoussilicon film) is formed on the laminate by plasma CVD at a temperatureof 300° C. using SiH₄ as material gas. The semiconductor film is 54 nm(preferably 25 to 80 nm) in thickness.

A base film 601 in this embodiment mode has a two-layer structure.However, the base insulating film may be a single layer or more than twolayers of insulating films. The material of the semiconductor film isnot limited but it is preferable to form the semiconductor film fromsilicon or a silicon germanium alloy (Si_(X)G_(1-X) (X=0.0001 to 0.02))by a known method (sputtering, LPCVD, plasma CVD, or the like). PlasmaCVD apparatus used may be one that processes wafer by wafer or one thatprocesses in batch. The base insulating film and the semiconductor filmmay be formed in succession in the same chamber to avoid contact withthe air.

The surface of the semiconductor film having an amorphous structure iswashed and then a very thin oxide film, about 2 nm in thickness, isformed on the surface using ozone water. Next, the semiconductor film isdoped with a minute amount of impurity element (boron or phosphorus) inorder to control the threshold of the TFTs. Here, the amorphous siliconfilm is doped with boron by ion doping in which diborane (B₂H₆) isexcited by plasma without mass separation. The doping conditions includesetting the acceleration voltage to 15 kV, the flow rate of gas obtainedby diluting diborane to 1% with hydrogen to 30 sccm, and the dose to2×10¹²/cm².

Next, a nickel acetate solution containing 10 ppm of nickel by weight isapplied by a spinner. Instead of application, nickel may be sprayed ontothe entire surface by sputtering.

The semiconductor film is subjected to heat treatment to crystallize itand obtain a semiconductor film having a crystal structure. The heattreatment is achieved in an electric furnace or by irradiation ofintense light. When heat treatment in an electric furnace is employed,the temperature is set to 500 to 650° C. and the treatment lasts for 4to 24 hours. Here, a silicon film having a crystal structure is obtainedby heat treatment for crystallization (at 550° C. for 4 hours) afterheat treatment for dehydrogenation (at 500° C. for an hour). Althoughthe semiconductor film is crystallized here by heat treatment using anelectric furnace, it may be crystallized by a lamp annealing apparatuscapable of achieving crystallization in a short time. This embodimentmode employs a crystallization technique in which nickel is used as ametal element for accelerating crystallization of silicon. However,other known crystallization techniques, solid phase growth and lasercrystallization, for example, may be employed.

Subsequently, after the oxide film of the surface of the silicon filmhaving a crystal structure was removed by dilute hydrofluoric acid orthe like, the irradiation of the first laser beam (XeCl: wavelength 308nm) for enhancing the crystallization ratio and repairing the defaultsremained within the crystal grain is performed in the air, or in theoxygen atmosphere. It is preferable that a solid-state laser of acontinuous oscillation or a pulse oscillation, a gas laser, or metalliclaser is used. Note that, as the solid-state laser, there may be given aYAG laser of a continuous oscillation or a pulse oscillation, a YVO₄laser, a YLF laser, a YAlO₃ laser, a glass laser, a ruby laser, analexandrite laser, a Ti: sapphire laser, and the like. As a the gaslaser, there may be given a excimer laser of continuous oscillation orpulse oscillation, Ar laser, Kr laser, CO₂ laser, or the like. And asthe metallic laser, there may be given a helium cadmium laser ofcontinuous oscillation or pulse oscillation, a copper vapor laser, or agold vapor laser. The laser beam may be used by converting into thesecond harmonic wave and the third harmonic wave by a nonlinear opticalelement. If a pulse laser beam is used, it is preferable that 10-10 kHzof repeated frequency and the relevant laser beam is condensed at100-150 mJ/cm² by an optical system, irradiated with overlap ratio of 50to 98% and it may be made it scan the surface of the silicon film. Here,the irradiation of the first laser beam is performed at repeatedfrequency of 30 Hz, 393 mJ/cm² of energy density in the air. At thismoment, if a continuous oscillation laser is used, about 0.01 to 100MW/cm² (preferably 0.1 to 10 MW/cm²) is necessary for the energy densityof laser beam. The substrate is relatively moved to the laser beam at aspeed of about 0.5 to 2000 cm/s. It should be noted that since it isperformed in the air, or in the oxygen atmosphere, an oxide film isformed on the surface by the irradiation of the first laser beam.

After removing an oxide film formed during irradiating the laser lightby using hydrofluoric acid, the second laser light is irradiated in anitrogen atmosphere or vacuum atmosphere to smooth the surface of thesemiconductor film. Above-described solid laser of the continuous laseror the pulse oscillation laser, the gas laser, or the metal laser may beused in that case. The laser light (the second laser light) can be usedby converting into the second higher harmonic or the third higherharmonics by nonlinear optical element. Note that the energy density ofthe second laser light is made larger than the energy density of thefirst laser light.

Laser light irradiation at this point is very important because it isused to form an oxide film to prevent doping of the silicon film havinga crystal structure with a rare gas element in later film formation bysputtering and because it enhances the gettering effect. The oxide filmformed by this laser light irradiation and an oxide film formed bytreating the surface with ozone water for 120 seconds together make abarrier layer that has a thickness of 1 to 5 nm in total.

Next, an amorphous silicon film containing argon is formed on thebarrier layer by sputtering to serve as a gettering site. The thicknessof the amorphous silicon film is 150 nm. The conditions for forming theamorphous silicon film here include setting the film formation pressureto 0.3 Pa, the gas (Ar) flow rate to 50 sccm, the film formation powerto 3 kW, and the substrate temperature to 150° C. The atomicconcentration of argon contained in the amorphous silicon film formedunder the above conditions is 3×10²⁰ to 6×10²⁰/cm³ and the atomicconcentration of oxygen thereof is 1×10¹⁹ to 3×10¹⁹/cm³. Thereafter,heat treatment is conducted in a lamp annealing apparatus at 650° C. for3 minutes for gettering.

Using the barrier layer as an etching stopper, the gettering site,namely, the amorphous silicon film containing argon, is selectivelyremoved. Then, the barrier layer is selectively removed by dilutedfluoric acid. Nickel tends to move toward a region having high oxygenconcentration during gettering, and therefore it is desirable to removethe barrier layer that is an oxide film after gettering.

Next, a thin oxide film is formed on the surface of the obtained siliconfilm containing a crystal structure (also referred to as a polysiliconfilm) using ozone water. A resist mask is then formed and the siliconfilm is etched to form island-like semiconductor layers separated fromone another and having desired shapes. After the semiconductor layersare formed, the resist mask is removed.

Also, after forming a semiconductor layer, in order to control thethreshold (Vth) of the TFTs, the semiconductor layers may be doped withan impurity element that gives the p-type or n-type conductivity.Impurity elements known to give a semiconductor the p-type conductivityare Group 13 elements in the periodic table, such as boron (B), aluminum(Al), and gallium (Ga). Impurity elements known to give a semiconductorthe n type conductivity are Group 15 elements in the periodic table,such as phosphorus (P) and arsenic (As).

Next, a thin oxide film is formed from ozone water on the surface of theobtained silicon film having a crystal structure (also called apolysilicon film). A resist mask is formed for etching to obtainsemiconductor layers 602 to 605 having desired shapes and separated fromone another like islands. After the semiconductor layers are obtained,the resist mask is removed. The oxide film is removed by an etchantcontaining fluoric acid, and at the same time, the surface of thesilicon film is washed. Then, an insulating film mainly containingsilicon is formed to serve as a gate insulating film 607. For formingthe gate insulating film 607, a lamination film formed by a siliconoxide film and silicon nitride film which are formed by sputteringmethod with Si as a target, a silicon oxynitride film which is formed byplasma CVD method, and silicon oxide film may be used. The gateinsulating film here is a silicon oxynitride film (composition ratio:Si=32%, O=59%, N=7%, H=2%) formed by plasma CVD to have a thickness of115 nm.

As shown in FIG. 10A, a first conductive film 608 with a thickness of 20to 100 nm and a second conductive film 609 with a thickness of 100 to400 nm are layered on the gate insulating film 607. In this embodimentmode, a 50 nm thick tantalum nitride film and a 370 nm thick tungstenfilm are layered on the gate insulating film 607 in the order stated.

The conductive materials of the first conductive film and secondconductive film are elements selected from the group consisting of Ta,W, Ti, Mo, Al, and Cu, or alloys or compounds mainly containing theabove elements. The first conductive film and the second conductive filmmay be semiconductor films, typically polycrystalline silicon films,doped with phosphorus or other impurity elements or may be Ag—Pd—Cualloy films. The present invention is not limited to a two-layerstructure conductive film. For example, a three-layer structureconsisting of a 50 nm thick tungsten film, 500 nm thick aluminum-siliconalloy (Al—Si) film, and 30 nm thick titanium nitride film layered inthis order may be employed. When the three-layer structure is employed,tungsten of the first conductive film may be replaced by tungstennitride, the aluminum-silicon alloy (Al—Si) film of the secondconductive film may be replaced by an aluminum-titanium alloy (Al—Ti)film, and the titanium nitride film of the third conductive film may bereplaced by a titanium film. Alternatively, a single-layer conductivefilm may be used.

As shown in FIG. 10B, resist masks 610 to 613 are formed by lightexposure to conduct the first etching treatment for forming gateelectrodes and wiring lines. The first etching treatment is conductedunder first and second etching conditions. ICP (inductively coupledplasma) etching is employed. The films can be etched into desired tapershapes by using ICP etching and adjusting etching conditions (the amountof power applied to a coiled electrode, the amount of power applied to asubstrate side electrode, the temperature of the substrate sideelectrode, etc.) suitably. Examples of the etching gas used includechlorine-based gas, typically, Cl₂, BCl₃, SiCl₄, or CCl₄, fluorine-basedgas, typically, CF₄, SF₆, or NF₃, and O₂.

The substrate side (sample stage) also receives an RF power of 150 W(13.56 MHz) to apply a substantially negative self-bias voltage. Thearea (size) of the substrate side electrode is 12.5 cm×12.5 cm and thecoiled electrode is a disc 25 cm in diameter (here, a quartz disc onwhich the coil is provided). The W film is etched under these firstetching conditions to taper it around the edges. Under the first etchingconditions, the rate of etching the W film is 200.39 nm/min., and therate of etching the TaN film is 80.32 nm/min. The selective ratio of Wto TaN is therefore about 2.5. The W film is tapered under the firstetching conditions at an angle of about 26°. Thereafter, the firstetching conditions are switched to the second etching conditions withoutremoving the resist masks 610 to 613. The second etching conditionsinclude using CF₄ and Cl₂ as etching gas, setting the gas flow rateratio thereof to 30:30 (sccm), and giving an RF (13.56 MHz) power of 500W to a coiled electrode at a pressure of 1 Pa to generate plasma foretching for about 30 seconds. The substrate side (sample stage) alsoreceives an RF power of 20 W (13.56 MHz) to apply a substantiallynegative self-bias voltage. Under the second etching conditionsincluding the use of a mixture of CF₄ and Cl₂, the TaN film and the Wfilm are etched to about the same degree. The rate of etching the W filmis 58.97 nm/min. and the rate of etching the TaN film is 66.43 nm/min.under the second etching conditions. In order to etch the films withoutleaving any residue on the gate insulating film, the etching time isprolonged by approximately 10 to 20%.

In the first etching treatment, first conductive layers and secondconductive layers are tapered around the edges by forming the resistmasks into proper shapes and by the effect of the bias voltage appliedto the substrate side. The angle of the tapered portions may be 15 to45°.

The first shape conductive layers 615 to 618 (the first conductivelayers 615 a to 618 a and the second conductive layers 615 b to 618 b)are formed that is consisted of the first conductive layer and thesecond conductive layer by the first etching treatment. The insulatingfilm 607 to be a gate insulating film is etched 10 to 20 nm, to form agate insulating film 620 having a region becoming thin where the firstshape conductive layers 615 to 618 do not overlap.

Next, a second etching process is conducted without removing the masksmade of resist. Here, SF₆, Cl₂ and O₂ are used as etching gases, theflow rate of the gases is set to 24/12/24 sccm, and RF (13.56 MHz) powerof 700 W is applied to a coil-shape electrode with a pressure of 1.3 Pato generate plasma, thereby performing etching for 25 seconds. RF (13.56MHz) power of 10 W is also applied to the substrate side (sample stage)to substantially apply a negative self-bias voltage. In the secondetching process, an etching rate to W is 227.3 n/min, an etching rate toTaN is 32.1 nm/min, a selection ratio of W to TaN is 7.1, an etchingrate to SiON that is the insulating film 620 is 33.7 nm/min, and aselection ratio of W to SiON is 6.83. In the case where SF₆ is used asthe etching gas, the selection ratio with respect to the insulating film620 is high as described above. Thus, reduction in the film thicknesscan be suppressed. In this embodiment, the film thickness of theinsulating film 620 is reduced by only about 8 nm.

By the second etching process, the taper angle of W becomes 70°. By thesecond etching process, second conductive layers 621 b to 624 b areformed. On the other hand, the first conductive layers are hardly etchedto become first conductive layers 621 a to 624 a. Note that the firstconductive layers 621 a to 624 a have substantially the same size as thefirst conductive layers 615 a to 615 a. In actuality, the width of thefirst conductive layer may be reduced by approximately 0.3 μm, namely,approximately 0.6 μm in the total line width in comparison with beforethe second etching process. However, there is almost no change in sizeof the first conductive layer.

Further, in the case where, instead of the two-layer structure, thethree-layer is structure is adopted in which a 50 nm thick tungstenfilm, an alloy film of aluminum and silicon (Al—Si) with a thickness of500 nm, and a 30 nm thick titanium nitride film are sequentiallylaminated, under the first etching conditions of the first etchingprocess in which: BCl₃, Cl₂ and O₂ are used as material gases; the flowrate of the gases is set to 65/10/5 (sccm); RF (13.56 MHz) power of 300W is applied to the substrate side (sample stage); and RF (13.56 MHz)power of 450 W is applied to a coil-shape electrode with a pressure of1.2 Pa to generate plasma, etching is performed for 117 seconds. As tothe second etching conditions of the first etching process, CF₄, Cl₂ andO₂ are used, the flow rate of the gases is set to 25/25/10 sccm, RF(13.56 MHz) power of 20 W is also applied to the substrate side (samplestage); and RF (13.56 MHz) power of 500 W is applied to a coil-shapeelectrode with a pressure of 1 Pa to generate plasma. With the aboveconditions, it is sufficient that etching is performed for about 30seconds. In the second etching process, BCl₃ and Cl₂ are used, the flowrate of the gases are set to 20/60 sccm, RF (13.56 Mhz) power of 100 Wis applied to the substrate side (sample stage), and RF (13.56 MHz)power of 600 W is applied to a coil-shape electrode with a pressure of1.2 Pa to generate plasma, thereby performing etching.

Next, the masks made of resist are removed, and then, a first dopingprocess is conducted to obtain the state of FIG. 1A. The doping processmay be conducted by ion doping or ion implantation. Ion doping isconducted with the conditions of a dosage of 1.5×10¹⁴ atoms/cm² and anaccelerating voltage of 60 to 100 keV. As an impurity element impartingn-type conductivity, phosphorus (P) or arsenic (As) is typically used.In this case, first conductive layers and second conductive layers 621to 624 become masks against the impurity element imparting n-typeconductivity, and first impurity regions 626 to 629 are formed in aself-aligning manner. The impurity element imparting n-type conductivityis added to the first impurity regions 626 to 629 in a concentrationrange of 1×10¹⁶ to 1×10¹⁷/cm³. Here, the region having the sameconcentration range as the first impurity region is also called an n⁻region.

Note that although the first doping process is performed after theremoval of the masks made of resist in this embodiment, the first dopingprocess may be performed without removing the masks made of resist.

Subsequently, as shown in FIG. 11B, masks 631 to 633 made of resist areformed, and a second doping process is conducted. The mask 631 is a maskfor protecting a channel forming region and a periphery thereof of asemiconductor layer forming a p-channel TFT of a driver circuit, themask 632 is a mask for protecting a channel forming region and aperiphery thereof of a semiconductor layer forming a TFT of a pixelportion.

With the ion doping conditions in the second doping process: a dosage of1.5×10¹⁵ atoms/cm²; and an accelerating voltage of 60 to 100 keV,phosphorus (P) is doped. Here, impurity regions are formed in therespective semiconductor layers in a self-aligning manner with thesecond conductive layer 621 b as masks. Of course, phosphorus is notadded to the regions covered by the masks 631 to 633. Thus, secondimpurity regions 634 and 635 and a third impurity region 637 are formed.The impurity element imparting n-type conductivity is added to thesecond impurity regions 634 and 635 in a concentration range of 1×10²⁰to 1×10²¹/cm³. Here, the region having the same concentration range asthe second impurity region is also called an n⁺ region.

Further, the third impurity region is formed at a lower concentrationthan that in the second impurity region by the first conductive layer,and is added with the impurity element imparting n-type conductivity ina concentration range of 1×10¹⁸ to 10¹⁹/cm³. Note that since doping isconducted by passing the portion of the first conductive layer having atapered shape, the third impurity region has a concentration gradient inwhich an impurity concentration increases toward the end portion of thetapered portion. Here, the region having the same concentration range asthe third impurity region is called an n⁻ region. Furthermore, theregions is covered by the mask 632 are not added with the impurityelement in the second doping process, and become first impurity region638.

Next, after the masks 631 to 633 made of resist are removed, masks 639and 640 made of resist are newly formed, and a third doping process isconducted as shown in FIG. 11C.

In the driver circuit, by the third doping process as described above,fourth impurity regions 641 and 642, and fifth impurity regions 643 and644 are formed in which an impurity element imparting p-typeconductivity is added to the semiconductor layer forming the p-channelTFT and to the semiconductor layer forming the storage capacitor.

Further, the impurity element imparting p-type conductivity is added tothe fourth impurity regions 641 and 642 in a concentration range of1×10²⁰ to 1×10²¹/cm³. Note that, in the fourth impurity regions 641 and642, phosphorus (P) has been added in the preceding step (n⁻ region),but the impurity element imparting p-type conductivity is added at aconcentration that is 1.5 to 3 times as high as that of phosphorus.Thus, the fourth impurity regions 641 and 642 have a p-typeconductivity. Here, the region having the same concentration range asthe fourth impurity region is also called a p⁺ region.

Further, fifth impurity regions 643 and 644 are formed in regionsoverlapping the tapered portion of the second conductive layers 622 aand 624 a, and are added with the impurity element imparting p-typeconductivity in a concentration range of 1×10¹⁸ to 1×10²⁰/cm³. Here, theregion having the same concentration range as the fifth impurity regionis also called a p⁻ region.

Through the above-described steps, the impurity regions having n-type orp-type conductivity are formed in the respective semiconductor layers.The conductive layers 621 to 624 become gate electrodes of a TFT.

Next, an insulating film (not shown) that covers substantially theentire surface is formed. In this embodiment, a 50 nm thick siliconoxide film is formed by plasma CVD. Of course, the insulating film isnot limited to a silicon oxide film, and other insulating filmscontaining silicon may be used in a single layer or a laminationstructure.

Then, a step of activating the impurity element added to the respectivesemiconductor layers is conducted. In this activation step, a rapidthermal annealing (RTA) method using a lamp light source, a method ofirradiating light emitted from a YAG laser or excimer laser from theback surface, heat treatment using a furnace, or a combination thereofis employed.

Further, although an example in which the insulating film is formedbefore the activation is shown in this embodiment mode, a step offorming the insulating film may be conducted after the activation isconducted.

Next, a first interlayer insulating film 645 is formed of a siliconnitride film, and heat treatment (300 to 550° C. for 1 to 12 hours) isperformed, thereby conducting a step of hydrogenating the semiconductorlayers. (FIG. 12A) The first interlayer insulating film 645 may be alamination structure consisting of the silicon nitride oxide film andthe silicon nitride film formed by the plasma CVD method. This step is astep of terminating dangling bonds of the semiconductor layers byhydrogen contained in the first interlayer insulating film 645. Thesemiconductor layers can be hydrogenated irrespective of the existenceof an insulating film (not shown) formed of a silicon oxide film.Incidentally, in this embodiment, a material containing aluminum as itsmain constituent is used for the second conductive layer, and thus, itis important to apply the heating process condition that the secondconductive layer can withstand in the step of hydrogenation. As anothermeans for hydrogenation, plasma hydrogenation (using hydrogen excited byplasma) may be conducted.

Next, a second interlayer insulating film 646 is formed from an organicinsulating material on the first interlayer insulating film 645. In thisembodiment, an acrylic resin film with a thickness of 1.6 μm is formed.

Furthermore, in order to prevent degassing such as oxygen, emission ofmoisture, and the like, generated from the inside of a layer insulationfilm on the second interlayer insulating film 646, the barrier film 647is formed. Specifically, the insulating film which contains aluminum,such as nitride aluminum (AlN), a nitride aluminum oxide (AlNO),oxidization nitride aluminum (AlNO), nitride silicon (SiN), and nitrideoxidization silicon (SiNO), or silicon, carbon nitride and DLC (diamondlike carbon) may be used to form the barrier film to have a thickness of0.2 to 1 μm. In this embodiment mode, the barrier film which consists ofnitride silicon is formed to have a thickness of 0.3 μm by thesputtering method. In addition, as a sputtering method used here, thereis the 2 pole sputtering method, an ion beam sputtering method, or theopposite target sputtering method.

Then, a contact hole that reaches each impurity region is formed. Inthis embodiment mode, a plurality of etching processes are sequentiallyperformed. In this embodiment mode, the second interlayer insulting filmis etched with the first interlayer insulating film as the etchingstopper, the first interlayer insulating film is etched with theinsulating film (not shown) as the etching stopper, and then, theinsulating film (not shown) is etched.

Wirings 650 to 656 and the first electrode 657 to be an anode are formedthat connect electrically with high concentration impurity regions 634,635, 641, and 642 respectively. In this embodiment mode, conductivematerials having light blocking effect are used. Specifically, aconductive nitride, an oxide, a carbide, a boride, and a silicide thatare composed of elements of fourth, fifth, or sixth group of theperiodic system can be used. However, wirings 650 to 656 and the firstelectrode (anode) 657 are patterned to be formed having a thickness of500 nm by using titanium nitride (TiN).

As the etching conditions of this embodiment mode, a mixed gas of CF₄and Cl₂ is used as an etching gas, the gas flow rate is set to 40/40sccm, and plasma is generated by applying a 450 W RF (13.56 MHZ) powerto a coil shape electrode is under 1.2 Pa to thereby perform etching forabout 30 seconds. A 100 W R (13.56 MHz) power is also applied to thesubstrate side (test piece stage) to effectively a negative self-biasvoltage.

In this embodiment, the first electrode (anode) 657 is formedsimultaneously with wiring formation, and to serve a function as awiring of high concentration impurity region 642.

As described above, a driver circuit 705 having an n-channel TFT 701 anda p-channel TFT 702, and pixel portion 706 having a switching TFT 703made from an n-channel TFT and a current control TFT 704 made from ann-channel TFT can be formed on the same substrate. (FIG. 12C) In thisspecification, the above substrate is called an active matrix substratefor the sake of convenience.

In the pixel portion 706, the switching TFT 703 (n-channel TFT) has achannel forming region 503, the first impurity region (n⁻ region) 638formed outside the conductive layer 623 forming the gate electrode, andthe second impurity region (n⁺ region) 635 functioning as a source ordrain region.

In the pixel portion 706, the TFT for current control 704 (p⁻ channelTFT) has a channel forming region 504, the fifth impurity region (p⁻region) 644 that overlaps a part of the conductive layer 624 forming thegate electrode through an insulating film, and the fourth impurityregion (p⁺ region) 642 functioning as a source or drain region.

Further, in the driver circuit 705, the n-channel TFT 701 has a channelforming region 501, the first impurity region (n⁻ region) 637 thatoverlaps a part of the conductive layer 621 forming the gate electrodethrough the insulating film, and to the second impurity region (n⁺region) 634 functioning as a source region or a drain region.

Further, in the driver circuit 705, the p-channel TFT 702 has a channelforming region 502, the fifth impurity region (p⁻ region) 643 thatoverlaps a part of the conductive layer 622 forming the gate electrodethrough the insulating film, and the fourth impurity region (p⁺ region)641 functioning as a source region or a drain region.

The above TFTs 701 and 702 are appropriately combined to form a shiftregister circuit, a buffer circuit, a level shifter circuit, a latchcircuit and the like, thereby forming the driver circuit 705. Forexample, in the case where a CMOS circuit is formed, the n-channel TFT701 and the p-channel TFT 702 may be complementarily connected to eachother.

Moreover, the structure of the n-channel TFT 701, which is a GOLD(Gate-drain Overlapped LDD) structure that is formed by overlapping aLDD (Lightly Doped Drain) region with a gate electrode, is appropriatefor the circuit in which the reliability takes top priority.

Note that the TFT (n-channel TFT and p-channel TFT) in the drivercircuit 705 are required to have a high driving capacity (on current:Ion) and prevent deterioration due to a hot carrier effect to therebyimprove reliability. A TFT having a region (GOLD region) where a gateelectrode overlaps a low concentration impurity region through a gateinsulating film is used as a structure effective in preventingdeterioration of an on current value due to hot carriers.

Note that the switching TFT 703 in the pixel portion 706 require a lowoff current (Ioff). A structure having a region (LDD region) where agate electrode does not overlap a low concentration impurity regionthrough a gate insulating film is used as a TFT structure for reducingan off current.

Next, an insulating film is formed to have a thickness of 1 μm. As theinsulating material containing silicon, silicon oxide, silicon nitride,or silicon oxide nitride may be used. As the organic resin, polyimide(including photosensitive polyimide), polyamide, acrylic (includingphotosensitive acrylic), BCB (benzocyclobutene), or the like may beused.

The opening portion is formed at the corresponding portion to the pixelelectrode 657 of the insulating film to form the insulating film 658(FIG. 13A).

In addition, an insulating film is formed using a photosensitivepolyimide to have a thickness of 1 μm, and after conducting a patterningby photolithography method the insulating film 658 is formed byconducting an etching treatment.

On the exposed first electrode (anode) 657 in the opening portion of theinsulating layer 658, an organic compound layer 659 is formed byevaporation method. (FIG. 13A) The organic compound layer 659 is formedby laminating same element structure as shown in Embodiment Mode 2.

Although only one pixel is shown here, one of the organic compound layeremitting three kinds of light, red, green, or blue is formed in eachpixel formed in plural in the pixel portion. Thus, full-color display isrealized. The combination of organic compounds forming organic compoundlayer that emits three kinds of light is described with reference toFIGS. 14A to 14D.

The light emitting element shown in FIG. 14A comprises a first electrode(anode) 1401, an organic compound layer 1402, and a second electrode(cathode) 1403. The organic compound layer 1402 has a laminationstructure of a hole transporting layer 1404, a light emitting layer1405, a blocking layer 1406, an electron transporting layer 1407, and anelectron transmitting region 1408. In addition, materials and thicknessof red luminescent light emitting element is shown in FIG. 14B,materials and thickness of green luminescent light emitting element isshown in FIG. 14C, and materials and thickness of blue luminescent lightemitting element is shown in FIG. 14D.

First, an organic compound layer emitting red light is formed.Specifically, the α-NPD as a hole transporting organic compound isformed into the hole transporting layer 1404 in a 40 nm film thickness.A 2,3,7,8,12,13,17,18-octaethyl-21H, 23H-porphyrin-platinum (hereinafterreferred to as the PtOEP) as a luminescent organic compound isco-deposited to form the light emitting layer 1405 with organiccompounds (hereinafter referred to as the host materials) a4,4′-dicarbazole-biphenyl (hereinafter referred to as the CBP) to serveas the host in a 30 nm film thickness. A basocuproin (hereinafterreferred to as the BCP) as a blocking organic compound is formed into ablocking layer 1406 in a 10 nm film thickness. Alq₃ as an electrontransporting organic compound is formed into an electron transportinglayer 1407 in a 40 nm film thickness. An electron transmitting region1408 is co-deposited to form a red luminescent organic compound layerwith TMB and Alq₃ in a 5 nm film thickness.

Although the case of forming a red luminescent organic compound layerusing 5 kinds of organic compounds with different functions is explainedhere, the present invention is not limited thereto, and known materialscan be used as the organic compound showing the red luminescence.

A green luminescent organic compound layer is formed. Specifically, anα-NPD as a hole transporting organic compound is formed into the holetransporting layer 1404 in a 40 nm film thickness. The light emittinglayer 1405 is formed by that a CBP used as a hole transmitting hostmaterial is co-deposited with a tris (2-phenyl pyridine) iridium(Ir(ppy)₃) in a 30 nm film thickness. A BCP as a blocking organiccompound is formed into the blocking layer 1406 in a 10 nm filmthickness. An Alq₃ as an electron transporting organic compound isformed into the electron transporting layer 1407 in a 40 nm filmthickness. The electron transmitting region 1408 is co-deposited to forma green luminescent organic compound layer with TMB and Alq₃ in a 5 nmfilm thickness.

Although the case of forming a green luminescent organic compound layerusing 4 kinds of organic compounds with different functions is explainedhere, the present invention is not limited thereto, and known materialscan be used as the organic compound showing the green luminescence.

A blue luminescent organic compound layer is formed. Specifically, anα-NPD as a luminescent organic compound and a hole transporting organiccompound is formed into the light emitting layer 1405 in a 40 nm filmthickness. A BCP as a blocking organic compound is formed into theblocking layer 1406 in a 10 nm film thickness. An Alq₃ as an electrontransporting organic compound is formed into the electron transportinglayer 1407 in a 40 nm film thickness. The electron transmitting region1408 is co-deposited to form a blue luminescent organic compound layerwith TMB and Alq₃ in a 5 nm film thickness.

Although the case of forming a blue luminescent organic compound layerusing 3 kinds of organic compounds with different functions is explainedhere, the present invention is not limited thereto, and known materialscan be used as the organic compound showing the blue light emission.

By forming the above-mentioned organic compounds on the first electrode(anode), an organic compound layer emitting the red luminescence, thegreen luminescence and the blue luminescence can be formed in the pixelportion.

Next, as shown in FIG. 13B, the second electrode (cathode) 660 is formedby overlapping the organic compound layer 659 and the insulating layer658. In this embodiment mode, the cathode 660 is formed by a conductivefilm that is transparent to the light. Specifically, it is preferablethat the cathode is formed by small work function material in order toimprove an electron injection. In this embodiment mode, the secondelectrode (cathode) 660 is made from aluminum or argentine.

In this embodiment mode, since the light generated at the light emittingelement radiates through the second electrode (cathode) 660, the cathodeneeds to be a transparent to the light. Therefore, the second electrode(cathode) 660 is made from aluminum by forming to have a thickness of 20nm.

Thus, the second electrode (cathode) 660 is formed by ultrathin film,thereby the electrode having light transparency can be formed. Thesecond electrode (cathode) 660 can be formed by another known materialonly in cases in which the material is a small work function materialand is a conductive film that is transparent to the light.

As shown in FIG. 13B, an element substrate having the first electrode(anode) 657 connected electrically to the current control TFT 704, theinsulating layer 658 formed between the first electrode (anode) 657 andthe electrode that is adjacent to the first electrode (anode) 657 (notillustrated), the organic compound layer 659 formed on the firstelectrode (anode) 657, and the light emitting element 661 made from thesecond electrode (cathode) 660 formed on the organic compound layer 659and the insulating layer 658 can be formed.

In this embodiment, the driving voltage of a TFT is 1.2 to 10 V,preferably 2.5 to 5.5 V.

When the display of the pixel portion is active (case of the movingpicture display), a background is displayed by pixels in which the lightemitting elements emit light and a character is displayed by pixels inwhich the light emitting elements do not emit light. However, in thecase where the moving picture display of the pixel portion is still fora certain period or more (referred to as a standby time in the presentspecification), for the purpose of saving electric power, it isappropriate that a display method is changed (inverted). Specifically, acharacter is displayed by pixels in which light emitting elements emitlight (also called a character display), and a background is displayedby pixels in which light emitting elements do not emit light (alsocalled a background display).

A detailed top surface structure of a pixel portion is shown in FIG.15A, and a circuit diagram thereof is shown in FIG. 15B. FIGS. 15A and15B denoted by a same reference numerals.

In FIGS. 15A and 15B, a switching TFT 1500 provided on a substrate isformed by using the switching TFT (n-channel type) TFT 703 of FIG. 13.Therefore, an explanation of the switching (n-channel type) TFT 703 maybe referred for an explanation of the structure. Further, a wiringindicated by reference numeral 1502 is a gate wiring for electricallyconnecting with gate electrodes 1501 (1501 a and 1501 b) of theswitching TFT 1500.

Note that, in this embodiment, a double gate structure is adopted, inwhich two channel forming regions are formed, but a single gatestructure, in which one channel forming region is formed, or a triplegate structure, in which three channel forming regions are formed, mayalso be adopted.

Further, a source of the switching TFT 1500 is connected to a sourcewiring 1503, and a drain thereof is connected to a drain wiring 1504.The drain wiring 1504 is electrically connected with a gate electrode1506 of a current control TFT 1505. Note that the current control TFT1505 is formed by using the current control (n-channel type) TFT 704 ofFIG. 13. Therefore, an explanation of the current control (n-channeltype) TFT 704 may be referred for an explanation of the structure. Notethat, although the single gate structure is adopted in this embodiment,the double gate structure or the triple gate structure may also beadopted.

Further, a source of the current control TFT 1505 is electricallyconnected with a current supply line 1507, and a drain thereof iselectrically connected with a drain wiring 1508. Besides, the drainwiring 1508 is electrically connected with the first electrode (cathode)1509 indicated by a dotted line.

A wiring indicated by reference numeral 1510 is a gate wiring connectedwith the gate electrode 1512 of the erasing TFT 1511. Further, a sourceof the erasing TFT 1511 is electrically connected to the current supplyline 1507, and a drain thereof is electrically connected to the drainwiring 1504.

The erasing TFT 1511 is formed like a current control TFT (n-channeltype) 704 in FIG. 13. Therefore, an explanation of the structure isreferred to that of the current control TFT (n-channel type) 704. Inthis embodiment, a single gate structure is described though, a doublegate structure or a triple gate structure can be used.

At this time, a storage capacitor (condenser) is formed in a regionindicated by reference numeral 1513. The capacitor 1513 is formed by asemiconductor film 1514 electrically connected with the current supplyline 1507, an insulating film (not shown) of the same layer as a gateinsulating film, and the gate electrode 1506. Further, a capacitorformed by the gate electrode 1506, the same layer (not shown) as a firstinterlayer insulating film, and the current supply line 1507 may be usedas a storage capacitor.

The light emitting element 1515 shown in circuit diagram in FIG. 15B iscomposed of the cathode 1509, an organic compound layer (notillustrated) formed on the cathode 1509, and an anode (not illustrated)formed on the organic compound layer. In the present invention, thecathode 1509 is connected with a source region and a drain region of thecurrent control TFT 1505.

A counter potential is supplied to the anode of the light emittingelement 1515. In addition, the power source potential is supplied to thepower supply line V. A potential difference between the counterpotential and the power source potential is always maintained at such alevel that causes the light emitting element to emit light when thepower source potential is applied to the pixel electrode. The powersource potential and the counter potential are supplied to the lightemitting device of the present invention by means of a power sourceprovided by an externally-attached IC chip or the like. In the presentspecification, the power source supplying a counter potential isreferred to as the counter power source 1516.

Embodiment Mode 7

Referring to FIGS. 16A and 16B, the external appearance of anactive-matrix type light-emitting device of the present invention willbe described in the embodiment mode. FIG. 16A is a top view of theluminescent device, and FIG. 16B is a sectional view taken on line A-A′of FIG. 16A. Shown by dotted lines, reference numeral 1601 represents asource signal line driving circuit, 1602, a pixel portion; and 1603, agate signal line driving circuit; 1604, a sealing substrate; and 1605, asealing agent. A space is surrounded by the sealing agent 1605.

Reference number 1608 represents an interconnection for transmittingsignals inputted to the source signal line driving circuit 1601 and thegate signal line driving circuit 1603. The interconnection 1608 receivesvideo signals or clock signals from a flexible print circuit (FPC) 1609,which will be an external input terminal. Only the FPC is illustrated,but a printed wiring board (PWB) may be attached to this FPC. Thelight-emitting device referred to in the present specification may bethe body of the light-emitting device, or a product wherein an FPC or aPWB is attached to the body.

The following will describe a sectional structure, referring to FIG.16B. The driving circuits and the pixel section are formed on thesubstrate 1610, but the source signal line driving circuit 1601 as oneof the driving circuits and the pixel section 1002 are shown in FIG.16B.

In the source signal line driving circuit 1601, a CMOS circuit whereinan n-channel type TFT 1623 and a p-channel type TFT 1624 are combined isformed. The TFTs constituting the driving circuit may be composed ofknown CMOS circuits, PMOS circuits or NMOS circuits. In this embodimentmode, a driver-integrated type, wherein the driving circuit is formed onthe substrate, is illustrated, but the driver-integrated type may notnecessarily be adopted. The driver may be fitted not to the substratebut to the outside.

The pixel portion 1602 is composed of a plurality of pixels each ofwhich includes a current control TFT 1611 and the first electrode 1612.The first electrode 1612 is electrically connected to a drain of thecurrent control TFT 1611.

An insulating layer 1613 is formed on each end of the first electrode1612. An organic compound layer composed of a first organic compoundlayer 1614 is formed on the first electrode 1612. The second electrode1616 is formed on the organic compound layer 1614. Thus completed is alight-emitting element 1618 composed of the first electrode 1612, theorganic compound layer 1614, and the second electrode 1616.

The second electrode 1616 also functions as a common wiring line sharedby all the pixels and is electrically connected to the FPC 1609 throughthe connection wiring line 1608.

The sealing substrate 1604 is bonded to the substrate 1610 with thesealing agent 1605 in order to seal the light-emitting element 1618formed over the substrate 1610. Spacers formed from a resin film may beprovided to keep the distance between the sealing substrate 1604 and thelight-emitting element 1618. The space 1607 inside the sealing agent1605 is filled with inert gas such as nitrogen. The sealing agent 1605is preferably an epoxy resin. Desirably, the material of the sealingagent 1605 is one that allows as little moisture and oxygen as possibleto transmit. A hygroscopic substance or an anti-oxidizing substance maybe placed in the space 1607.

In this embodiment, a glass substrate or a quartz substrate is used asthe sealing substrate 1604. Alternatively, the cover member may be aplastic substrate that is formed of FRP (fiberglass-reinforcedplastics), PVF (polyvinyl fluoride), Mylar, polyester, acrylic, or thelike. After the sealing substrate 1604 is bonded to the substrate 1610using the sealing agent 1605, the side faces (exposed faces) of thedevice may be further covered and sealed by the sealing agent.

By sealing the light-emitting element in the space 1607 as describedabove, the light-emitting element is completely shut off from theoutside and external substances that accelerate degradation of theorganic compound layer, such as moisture and oxygen, can be preventedfrom entering the light-emitting element. Therefore, a highly reliablelight-emitting device can be obtained.

The structure of this embodiment may be freely combined with any of thestructures of Embodiment Modes 1 to 6.

Embodiment Mode 8

In this embodiment, a case in which a passive type (simple matrix type)light emitting device having an element structure of the presentinvention is manufactured is described with reference to FIG. 17. InFIG. 17, reference numbers 1701 and 1702 represent a glass substrate andthe first electrode (anode) made of a metal compound film, respectively.In this embodiment, TiN is formed by sputtering as metal compounds. Notshown in FIG. 17, plural anodes are arranged in the stripe form inparallel with the paper. In the passive matrix light emitting device,since the anode material is required higher conductivity than activematrix light emitting device, it is effective that higher conductivemetal compounds than ITO that is used conventionally is used for theanode in reducing the driving voltage of the light emitting element.

Banks 1703 made of an insulating material are formed to cross the firstelectrode (anode) 1702 arranged in the stripe form. The banks 1703 areformed perpendicularly to the paper face to contact the first electrode(anode) 1702.

Next, a layer comprising at least one organic compound 1704 is formed.As the material which makes the layer comprising at least one organiccompound 1704, a known material which can give luminescence, as well asthe materials described in this specification can be used.

For example, by forming a layer comprising at least one organic compoundgiving red luminescence, a layer comprising at least one organiccompound giving green luminescence, and a layer comprising at least oneorganic compound giving blue luminescence, a light emitting devicegiving three types of luminescence rays can be formed. Since the layercomprising at least one organic compound 1704 composed of these layersis formed along grooves made in the banks 1703, the layer 1704 isarranged in the stripe form perpendicular to the paper face.

Next, the second electrode (cathode) 1705 is formed on the organiccompound layer 1704. The second electrode (cathode) 1705 is formed byvapor deposition using a metal mask.

Since the lower first electrode (anode) 1702 is made from transparentmaterials in this embodiment mode, light generated at the layercomprising at least one organic compound layer 1704 is radiated upwardfrom second electrode (cathode) 1705.

Next, a glass substrate is prepared as a sealing substrate 1707. Sincethe sealing substrate 1707 may have transparency in the structure ofthis embodiment, a substrate made of plastic or quartz may be used aswell as glass substrate.

The sealing substrate 1707 is adhered to the substrate 1701 with asealant 1708 made of an ultraviolet hardening resin. The inside 1706 ofthe sealant 1708 is an airtightly-closed space, and the inside is filledwith an inert gas such as nitrogen or argon. It is effective to put amoisture absorbent, a typical example of which is barium oxide, in theairtightly closed space 1706. At last, a flexible printed circuit (FPC)1709 is fitted to the anodes to complete a passive type light emittingdevice.

This embodiment mode may be carried out by combining except structuresrelevant to the element structure (active matrix type) shown inEmbodiment Modes 1 to 7.

Embodiment Mode 9

Being self-luminous, a light emitting device using a light emittingelement has better visibility in bright places and wider viewing anglethan liquid crystal display devices. Therefore, various electricappliances can be completed by using the light emitting device of thepresent invention.

Given as examples of an electric appliance that employs a light emittingdevice manufactured in accordance with the present invention are videocameras, digital cameras, goggle type displays (head mounted displays),navigation systems, audio reproducing devices (such as car audio andaudio components), notebook computers, game machines, portableinformation terminals (such as mobile computers, cellular phones,portable game machines, and electronic books), and image reproducingdevices equipped with recording media (specifically, devices is with adisplay device that can reproduce data in a recording medium such as adigital video disk (DVD) to display an image of the data). Wide viewingangle is important particularly for portable information terminalsbecause their screens are often slanted when they are looked at.Therefore it is preferable for portable information terminals to employthe light emitting device using the light emitting element. Specificexamples of these electric appliance are shown in FIGS. 18A to 18H.

FIG. 18A shows a display device, which is composed of a case 2001, asupport base 2002, a display unit 2003, speaker units 2004, a videoinput terminal 2005, etc. The light emitting device manufactured inaccordance with the present invention can be applied to the display unit2003. Since the light emitting device having the light emitting elementis self-luminous, the device does not need back light and can make athinner display unit than liquid crystal display devices. The displaydevice refers to all display devices for displaying information,including ones for personal computers, for TV broadcasting reception,and for advertisement.

FIG. 18B shows a digital still camera, which is composed of a main body2101, a display unit 2102, an image receiving unit 2103, operation keys2104, an external connection port 2105, a shutter 2106, etc. The lightemitting device manufactured in accordance with the present inventioncan be applied to the display unit 2102.

FIG. 18C shows a notebook personal computer, which is composed of a mainbody 2201, a case 2202, a display unit 2203, a keyboard 2204, anexternal connection port 2205, a pointing mouse 2206, etc. The lightemitting device manufactured in accordance with the present inventioncan be applied to the display unit 2203.

FIG. 18D shows a mobile computer, which is composed of a main body 2301,a display unit 2302, a switch 2303, operation keys 2304, an infraredport 2305, etc. The light emitting device manufactured in accordancewith the present invention can be applied to the display unit 2302.

FIG. 18D shows a portable image reproducing device equipped with arecording medium (a DVD player, to be specific). The device is composedof a main body 2401, a case 2402, a display unit A 2403, a display unitB 2404, a recording medium (DVD or the like) reading unit 2405,operation keys 2406, speaker units 2407, etc. The display unit A 2403mainly displays image information whereas the display unit B 2404 mainlydisplays text information. The light emitting device manufactured inaccordance with the present invention can be applied to the displayunits A 2403 and B 2404. The image reproducing device equipped with arecording medium also includes home-video game machines.

FIG. 18F shows a goggle type display (head mounted display), which iscomposed of a main body 2501, display units 2502, and arm units 2503.The light emitting device manufactured in accordance with the presentinvention can be applied to the display units 2502.

FIG. 16G shows a video camera, which is composed of a main body 2601, adisplay unit 2602, a case 2603, an external connection port 2604, aremote control receiving unit 2605, an image receiving unit 2606, abattery 2607, an audio input unit 2608, operation keys 2609, eye pieceportion 2610 etc. The light emitting device manufactured in accordancewith the present invention can be applied to the display unit 2602.

FIG. 16H shows a portable telephone, which is composed of a main body2701, a case 2702, a display unit 2703, an audio input unit 2704, anaudio output unit 2705, operation keys 2706, an external connection port2707, an antenna 2708, etc. The light emitting device manufactured inaccordance with the present invention can be applied to the display unit2703. If the display unit 2703 displays white letters on blackbackground, the cellular phone consumes less power.

If the luminance of light emitted from organic materials is raised infuture, the light emitting device can be used in front or rearprojectors by enlarging outputted light that contains image informationthrough a lens or the like and projecting the light.

These electric appliances now display with increasing frequencyinformation sent through electronic communication lines such as theInternet and CATV (cable television), especially, animation information.Since organic materials have very fast response speed, the lightemitting device is suitable for animation display.

In the light emitting device, light emitting portions consume power andtherefore it is preferable to display information in a manner thatrequires less light emitting portions. When using the light emittingdevice in display units of portable information terminals, particularlycellular phones and audio reproducing devices that mainly display textinformation, it is preferable to drive the device such that non-lightemitting portions form a background and light emitting portions formtext information.

As described above, the application range of the light emitting devicemanufactured by using the deposition device of the present invention isso wide that it is applicable to electric appliances of any field. Theelectric appliances of this embodiment can be completed by using thelight emitting device formed by implementing Embodiment Modes 1 to 8.

Embodiment Mode 10

In addition, it is also possible for the light emitting device of thepresent invention to be given the structure shown in FIG. 19. Note thatFIG. 19 is used in explaining a case of a structure in which a firstelectrode 1911 is an anode, a second electrode 1914 is a cathode, andlight passes through from the first electrode 1911 side, as explained inEmbodiment Mode 4. Reference numeral 1901 denotes a substrate, 1902denotes a channel formation region, 1903 denotes a source region, 1904denotes a drain region, 1905 denotes a gate insulating film, 1906denotes a gate electrode, 1908 denotes an interlayer insulating film,1921 denotes a switching TFT, 1922 denotes a current control TFT, and1917 denotes a barrier film.

Materials such as an inorganic material (silicon oxide, silicon nitride,silicon oxynitride, or the like), a photosensitive or non-photosensitiveorganic material (polyimide, acrylic, polyamide, polyimide amide,resist, or benzocyclobutene), a laminate of these materials can be usedas an insulating layer 1912 (referred to as bank, partition, barrier,and the like) covering an edge portion of the first electrode (anode)1911 (and a wiring 1907). For example, it is preferable that the radiusof curvature in an edge portion of the insulating film be set to 0.2 to2 μm as shown in FIG. 19 for a case of using a positive typephotosensitive acrylic as an organic resin material, and that a curvedsurface having an angle with the contact surface equal to or greaterthan 35 be provided.

Furthermore, an organic compound layer 1913 is an extremely thin film,and therefore it is preferable that the surface of the first electrode1911 be leveled. For example, leveling may be performed by chemically ormechanically polishing (typically a CMP technique), or another processeither before or after patterning of the first electrode 1911. Further,cleaning (brush cleaning or sponge cleaning) is performed in order toremove foreign substances (such as refuse) before and after formation ofthe insulating layer 1912 in order to increase the cleanliness of thesurface of the first electrode 1911. The generation of dark spots andpoint defects is thus reduced.

In addition to the materials shown in previous embodiment modes,materials emitting a white light can also be used in the organiccompound layer 1913 of a light emitting element 1915. In this case,Alq₃, Alq₃ into which the red color pigment nile red is partially doped,Alq₃, p-EtTAZ, and TPD (aromatic diamine) may be laminated in order fromthe first electrode (anode) 1911 by using evaporation. Note that R(red), G (green), and B (blue) color lights can also be obtained whenusing white color luminescence by combining color filters in thestructure.

Further, the second electrode (cathode) 1914 is formed on the organiccompound layer 1913, and evaporation (resistance heating) and sputteringcan be used as film formation methods, The light emitting element 1915made from the first electrode (anode) 1911, the organic compound layer1913, and the second electrode (cathode) 1914 can thus be formed.

In addition, a passivation film 1916 can also be formed on the secondelectrode (cathode) 1914 of the light emitting element 1915 by using amaterial having insulating characteristics. Note that in addition to asilicon nitride film formed by sputtering using Si as a target, alaminate film in which a hygroscopic material is sandwiched by a siliconnitride film can also be used as the passivation film 1916 material. Inaddition, it is also possible to use a DLC film (diamond like carbonfilm), carbon nitride (CxNy), and the like.

The present invention can improve the characteristics of a lightemitting element, without imparting adverse influence to TFTcharacteristics in an active matrix light emitting device having TFTs.This is because donor levels positioned in intermediate LUMO levelsbetween a cathode and an organic compound layer are formed, and thetransmission of electrons injected from the cathode can be performedwith good efficiency by forming an electron transmitting regioncontaining donor molecules in a portion of the organic compound layer,and by forming the electron transmitting region so that it contacts thecathode.

In addition, energy generated due to carrier recombination in a lightemitting layer is transferred to an electric charge transfer complexdeveloping in the electron to transmitting region containing the donormolecules, and extinguishing of light of the light emitting elements canbe prevented and degradation in the light emission efficiency can beprevented by forming the electron transmitting region such that it doesnot contact the light emitting layer contained in the organic compoundlayer.

1-15. (canceled)
 16. A light emitting device comprising: a firstelectrode over a substrate; a hole transporting layer on the firstelectrode; a light emitting layer over the hole transporting layer; anelectron transporting layer comprising a material having electrontransporting characteristics on the light emitting layer; and a secondelectrode on the electron transporting layer, wherein at least a portionof the electron transporting layer is an electron transmitting region,the electron transmitting region comprising donor molecules, wherein theelectron transmitting region is in contact with the second electrode andis not in contact with the light emitting layer, wherein at least aportion of the hole transporting layer is a hole transmitting region,the hole transmitting region comprising acceptor molecules, and whereinthe second electrode is light transmitting.
 17. A light emitting deviceaccording to claim 16, wherein the first electrode is an anode and thesecond electrode is a cathode.
 18. A light emitting device according toclaim 16, further comprising a TFT having a source region and a drainregion formed over the substrate.
 19. A light emitting device accordingto claim 18, wherein the first electrode is electrically connected toone of the source region and the drain region.
 20. A light emittingdevice according to claim 16, wherein the donor molecule is3,3′,5,5′-tetramethylbenzidine.
 21. A light emitting device according toclaim 16, wherein the light emitting device is incorporated in at leastone selected from the group consisting of a display device, a digitalcamera, a personal computer, a mobile computer, a portable imageplayback device prepared with a recording medium, a goggle type display,a video camera and a portable telephone.
 22. A light emitting deviceaccording to claim 16, wherein the donor molecules contain an organiccompound.
 23. A light emitting device according to claim 16, wherein thedonor molecules contain tetrathiotetracene and the material havingelectron transporting characteristics contains Alq₃.
 24. A lightemitting device according to claim 16, wherein the electron transmittingregion comprises the material having electron transportingcharacteristics.
 25. A light emitting device according to claim 16,wherein the hole transmitting region is in contact with the firstelectrode and is not in contact with the light emitting layer.
 26. Alight emitting device comprising: a first electrode over a substrate; ahole transporting layer on the first electrode; a light emitting layerover the hole transporting layer; an electron transporting layercomprising a material having electron transporting characteristics onthe light emitting layer; and a second electrode on the electrontransporting layer, wherein at least a portion of the electrontransporting layer is an electron transmitting region, the electrontransmitting region comprising donor molecules, wherein the electrontransmitting region is in contact with the second electrode and is notin contact with the light emitting layer, wherein at least a portion ofthe hole transporting layer is a hole transmitting region, the holetransmitting region comprising acceptor molecules, and wherein the lightemitting layer includes triplet light emission materials.
 27. A lightemitting device according to claim 26, wherein the first electrode is ananode and the second electrode is a cathode.
 28. A light emitting deviceaccording to claim 26, further comprising a TFT having a source regionand a drain region formed over the substrate.
 29. A light emittingdevice according to claim 28, wherein the first electrode iselectrically connected to one of the source region and the drain region.30. A light emitting device according to claim 26, wherein the donormolecule is 3,3′,5,5′-tetramethylbenzidine.
 31. A light emitting deviceaccording to claim 26, wherein the light emitting device is incorporatedin at least one selected from the group consisting of a display device,a digital camera, a personal computer, a mobile computer, a portableimage playback device prepared with a recording medium, a goggle typedisplay, a video camera and a portable telephone.
 32. A light emittingdevice according to claim 26, wherein the donor molecules contain anorganic compound.
 33. A light emitting device according to claim 26,wherein the donor molecules contain tetrathiotetracene and the materialhaving electron transporting characteristics contains Alq₃.
 34. A lightemitting device according to claim 26, wherein the electron transmittingregion comprises the material having electron transportingcharacteristics.
 35. A light emitting device according to claim 26,wherein the second electrode is light transmitting.
 36. A light emittingdevice according to claim 26, wherein the hole transmitting region is incontact with the first electrode and is not in contact with the lightemitting layer.
 37. A light emitting device comprising: a light emittingelement, the light emitting element comprising: a first electrode over asubstrate; a hole transporting layer on the first electrode; a lightemitting layer over the hole transporting layer; an electrontransporting layer comprising a material having electron transportingcharacteristics on the light emitting layer; and a second electrode onthe electron transporting layer, wherein at least a portion of theelectron transporting layer is an electron transmitting region, theelectron transmitting region comprising donor molecules, wherein theelectron transmitting region is in contact with the second electrode andis not in contact with the light emitting layer, wherein at least aportion of the hole transporting layer is a hole transmitting region,the hole transmitting region comprising acceptor molecules, and whereinthe light emitting element emits a white light.
 38. A light emittingdevice according to claim 37, wherein the first electrode is an anodeand the second electrode is a cathode.
 39. A light emitting deviceaccording to claim 37, further comprising a TFT having a source regionand a drain region formed over the substrate.
 40. A light emittingdevice according to claim 39, wherein the first electrode iselectrically connected to one of the source region and the drain region.41. A light emitting device according to claim 37, wherein the donormolecule is 3,3′,5,5′-tetramethylbenzidine.
 42. A light emitting deviceaccording to claim 37, wherein the light emitting device is incorporatedin at least one selected from the group consisting of a display device,a digital camera, a personal computer, a mobile computer, a portableimage playback device prepared with a recording medium, a goggle typedisplay, a video camera and a portable telephone.
 43. A light emittingdevice according to claim 37, wherein the donor molecules contain anorganic compound.
 44. A light emitting device according to claim 37,wherein the donor molecules contain tetrathiotetracene and the materialhaving electron transporting characteristics contains Alq₃.
 45. A lightemitting device according to claim 37, wherein the electron transmittingregion comprises the material having electron transportingcharacteristics.
 46. A light emitting device according to claim 37,wherein the second electrode is light transmitting.
 47. A light emittingdevice according to claim 37, wherein the hole transmitting region is incontact with the first electrode and is not in contact with the lightemitting layer.
 48. A light emitting device comprising: a firstelectrode over a substrate; a hole transporting layer on the firstelectrode; a light emitting layer over the hole transporting layer, anelectron transporting layer comprising a material having electrontransporting characteristics on the light emitting layer; and a secondelectrode on the electron transporting layer, wherein at least a portionof the electron transporting layer includes a region which comprisesdonor molecules, wherein the region which comprises donor molecules isin contact with the second electrode and is not in contact with thelight emitting layer, wherein at least a portion of the holetransporting layer includes a region which comprises acceptor molecules,and wherein the second electrode is light transmitting.
 49. A lightemitting device according to claim 48, wherein the first electrode is ananode and the second electrode is a cathode.
 50. A light emitting deviceaccording to claim 48, further comprising a TFT having a source regionand a drain region formed over the substrate.
 51. A light emittingdevice according to claim 50, wherein the first electrode iselectrically connected to one of the source region and the drain region.52. A light emitting device according to claim 48, wherein the donormolecule is 3,3,5,5′-tetramethylbenzidine.
 53. A light emitting deviceaccording to claim 48, wherein the light emitting device is incorporatedin at least one selected from the group consisting of a display device,a digital camera, a personal computer, a mobile computer, a portableimage playback device prepared with a recording medium, a goggle typedisplay, a video camera and a portable telephone.
 54. A light emittingdevice according to claim 48, wherein the donor molecules contain anorganic compound.
 55. A light emitting device according to claim 48,wherein the donor molecules contain tetrathiotetracene and the materialhaving electron transporting characteristics contains Alq₃.
 56. A lightemitting device according to claim 48, wherein the region whichcomprises acceptor molecules is in contact with the first electrode andis not in contact with the light emitting layer.
 57. A light emittingdevice comprising: a first electrode over a substrate; a holetransporting layer on the first electrode; a light emitting layer overthe hole transporting layer, an electron transporting layer comprising amaterial having electron transporting characteristics on the lightemitting layer; and a second electrode on the electron transportinglayer, wherein at least a portion of the electron transporting layerincludes a region which comprises donor molecules, wherein the regionwhich comprises donor molecules is in contact with the second electrodeand is not in contact with the light emitting layer, wherein at least aportion of the hole transporting layer includes a region which comprisesacceptor molecules, and wherein the light emitting layer includestriplet light emission materials.
 58. A light emitting device accordingto claim 57, wherein the first electrode is an anode and the secondelectrode is a cathode.
 59. A light emitting device according to claim57, further comprising a TFT having a source region and a drain regionformed over the substrate.
 60. A light emitting device according toclaim 59, wherein the first electrode is electrically connected to oneof the source region and the drain region.
 61. A light emitting deviceaccording to claim 57, wherein the donor molecule is3,3′,5,5′-tetramethylbenzidine.
 62. A light emitting device according toclaim 57, wherein the light emitting device is incorporated in at leastone selected from the group consisting of a display device, a digitalcamera, a personal computer, a mobile computer, a portable imageplayback device prepared with a recording medium, a goggle type display,a video camera and a portable telephone.
 63. A light emitting deviceaccording to claim 57, wherein the donor molecules contain an organiccompound.
 64. A light emitting device according to claim 57, wherein thedonor molecules contain tetrathiotetracene and the material havingelectron transporting characteristics contains Alq₃.
 65. A lightemitting device according to claim 57, wherein the second electrode islight transmitting.
 66. A light emitting device according to claim 57,wherein the region which comprises acceptor molecules is in contact withthe first electrode and is not in contact with the light emitting layer.67. A light emitting device comprising: a light emitting element, thelight emitting element comprising: a first electrode over a substrate; ahole transporting layer on the first electrode; a light emitting layerover the hole transporting layer, an electron transporting layercomprising a material having electron transporting characteristics onthe light emitting layer; and a second electrode on the electrontransporting layer, wherein at least a portion of the electrontransporting layer includes a region which comprises donor molecules,wherein the region which comprises donor molecules is in contact withthe second electrode and is not in contact with the light emittinglayer, wherein at least a portion of the hole transporting layerincludes a region which comprises acceptor molecules, and wherein thelight emitting element emits a white light.
 68. A light emitting deviceaccording to claim 67, wherein the first electrode is an anode and thesecond electrode is a cathode.
 69. A light emitting device according toclaim 67, further comprising a TFT having a source region and a drainregion formed over the substrate.
 70. A light emitting device accordingto claim 69, wherein the first electrode is electrically connected toone of the source region and the drain region.
 71. A light emittingdevice according to claim 67, wherein the donor molecule is3,3′,5,5′-tetramethylbenzidine.
 72. A light emitting device according toclaim 67, wherein the light emitting device is incorporated in at leastone selected from the group consisting of a display device, a digitalcamera, a personal computer, a mobile computer, a portable imageplayback device prepared with a recording medium, a goggle type display,a video camera and a portable telephone.
 73. A light emitting deviceaccording to claim 67, wherein the donor molecules contain an organiccompound.
 74. A light emitting device according to claim 67, wherein thedonor molecules contain tetrathiotetracene and the material havingelectron transporting characteristics contains Alq₃.
 75. A lightemitting device according to claim 67, wherein the second electrode islight transmitting.
 76. A light emitting device according to claim 67,wherein the region which comprises acceptor molecules is in contact withthe first electrode and is not in contact with the light emitting layer.